A generic diagnosis is given together with notes on infraspecific variation of known species in the subgenera Pterygosoma Peters, 1849, and Gerrhosaurobia Lawrence, 1958, and first descriptions of the following hitherto unrecorded stages. Males of P. transvaalensis, P. triangulare, P. hirsti hirsti, P. melanum melanum, P. melanum longipalpe, P. agamae aculeatum and P. persicum; nymphae of P. transvaalense, P. neumanni, P. agamae agamae and P. persicum; larvae of P. neumanni and P. agamae agamae. The following species are here considered to be subspecies: P. hirsti bedfordi Lawrence, 1936, P. melanum longipalpe Lawrence, 1936, P. agamae aculeatum Lawrence, 1936. The following species are reduced to synonymy: P. neumanni hirstielli Abdussalam, 1941 (= P. neumanni Berlese, 1910), P. rubicundum Lawrence, 1958 (= P. agamae agamae Peters, 1849). Three subspecies and two species are described for the first time, namely, P. fimbriata problematica, P. melanum angolae, P. melanum capensis, P. benguellae and P. spinosa. A list of parasitized lizard species with their scale-mite parasites is presented together with unparasitized lizard species of the Gerrhosauridae and the agamid genera Calotes and Agama. Support is given to Lawrence's (1936) conclusions on the factors preventing parasitization of the lizards. This is followed by a brief discussion of host-parasite relations and similarities between different species are evinced.

Sincere thanks are tendered to Dr A. J. Hesse, Chief Entomologist, South African Museum, for the loan of paratype material of many species; to Dr R. F. Lawrence for making available slides of P. fimbriata, P. (G.) gerrhosauri and co-types of P. rubicundum; to Dr G. O. Evans, British Museum (Nat. Hist.), for advice and for the loan of Hirst's material of P. agamae, P. persicum, P. neumanni and P. inermis; to Mr J. C. Battersby and Miss Alice Grandison of the Reptile Section of the British Museum (Nat. Hist.) for facilitating the collection of parasites from the lizards under their care; and finally to Mr T. E. Hughes and Dr F. A. Turk for their invaluable advice and encouragement.

1. The hatching of N. battus under laboratory conditions was investigated. A high hatch of ripe eggs was obtained on exposure to constant temperatures in the approximate range 8–15° C., and very little hatching took place at temperatures outside this range.

2. These, and other published results can be explained in terms of a hypothesis transferred from the study of the breaking of insect diapause. This hypothesis supposes that two processes underly the completion of hatching—a cold process with low temperature optimum and a warm process with a higher temperature optimum and which can only proceed as the cold process is completed.

3. It is not easy to apply these findings directly to field events, but the attempt to do so leads to the suggestion that the apparent synchrony of hatching and the presence of susceptible lamb hosts in the north-east of the British Isles may be partly fortuitous, and that in slightly different climatic circumstances many eggs might hatch in the autumn or during the winter.

I wish to thank Mr A. V. Cunningham of Threepwood, Galashiels, and Mr J. M. M. Cunningham of the Edinburgh School of Agriculture for their generous help in making sampling of their flocks possible, and Dr J. T. Stamp for advice on the presentation of this paper.

Opisthogynidae fam.nov. is erected for a group of Gastrocotyloidea Price (1959), in which the gastrocotylid clamps are limited to the four primary pairs, the ovarian field is posterior to the main testicular field, and the cuticle is finely plicated, producing forward-pointing serrations along the margins of the hind body. Opisthogyninae subfam.nov. have a slightly asymmetrical haptor due to unequal lengths of clamps and their pedicels, or to one row being sessile on glandular pads which may be confluent as a thick shelf on one side only. The clamps have an incipient internal asymmetry, the adaxial sector being the more developed. Opisthogyne keralae gen. et sp.nov., on Sphyraena acutipennis: with subequal clamps unequally pedunculated, retains the protohaptor with three pairs of anchors; the muscular penis opens in a lateral atrium, and the median dorsal vagina is unarmed. Gemmaecaputia corrugata Tripathi, 1959, and G. brinkmannii sp.nov., both on Sphyraena obtusata, have each a very conspicuous pre-oral gland-mass. They have unequally disposed and asymmetrical clamps on stalks but lack a protohaptor and anchors. The genital terminalis is similar. The genotype Gemmaecaputia corrugata is redescribed. The new species G. brinkmannii differs in having some post-ovarial testes, in the muscular penis being less heavily cuticularized and the egg being smaller; yet it is nearly twice the size of the genotype, and its pre-oral glands are in two groups of two rows, instead of a single continuous row. Both Allodiscocotyla chorinemi Yamag., 1953 and A. diacanthi sp.nov., occur on Chorinemus sanctipetri. In both of these, unlike the last two genera, the asymmetrical clamps have ribs in the walls. One row of clamps is sessile, on a shelf, or on separate pads, and the other is short-stalked. The protohaptor is retained by the adult. There is a median spiny eversible cirrus and a single lateral unarmed vagina. The genotype is redescribed from a new host. The new species differs in its four separate clamppads on one side, the opposite row being subsessile. There is only one pair of anchors (the largest) instead of three pairs; there are no par-ovarial testes (all are preovarial), and the internal details of the clamps differ. Pseudomazocraes Caballero & Bravo Hollis, 1955, is compared with and included in the Opisthogyninae. Pentatrinae subfam.nov. is erected for Pentatres sphyraenae Euzet & Razarihelisoa, 1959, since its gastrocotylid clamps are modified like those of Priceinae (Gastrocotylidae), but are internally symmetrical and disposed in an asymmetrical fringing-arc round the hind body; the three larger clamps are pedunculated. The muscular penis and atrium are sublateral. Vallisiinae Price, 1943, is emended to include only Vallisia and Vallisiopsis, with highly developed somatic asymmetry. Slight asymmetry is seen in the short-stalked clamps which are usually shifted backwards from the sessile row, the clamps of which are either near three marginal tabs separated by glandular clefts, or on four pads. The clamps themselves are symmetrical and gastrocotylid with ribs in the walls, but without extra effective sclerites. The protohaptor is broad and has one pair of anchors. In all there is a long median spiny eversible cirrus. Vallisia indica sp.nov. from Chorinemus sanctipetri, has sessile clamps on four separate pads and is nearest to Vallisia chorinemi Yamag. This latter, however, has three marginal tabs for the sessile clamps and the combs in the two lateral vaginae are different. V. indica has only half the number of testes and lacks oesophageal diverticula.

Protomicrocotyloidea sup.fam.nov. is created and defined to include aberrant discocotyline forms in which the protohaptor is secondarily developed as a main holdfast. This is a transverse musculo-glandular organ retaining the three dissimilar pairs of larval anchors. The other main holdfast is the unique posteriorlateral glandular pit with projecting muscular lips, just anterior-dorsal to the relatively feeble clamps, which may be gastrocotylid or discocotylid, some always being inhibited. Carangixenus gen.nov. erected for Protomicrocotyle celebensis Yamag., 1953, shares Protomicrocotylinae with Protomicrocotyle mirabilis (MacCallum), since both have gastrocotylid clamps, but in the former they have additional sclerites and an asymmetry approaching that of Gotocotyla spp. (Gastrocotylidae). In Abortipedinae subfam.nov. the muscular protohaptor has anchor-like lobes at each end as in Protomicrocotylinae, but the four clamps on the uninhibited side of the euhaptor are simple discocotylid and without ribs in the capsule walls. The genital terminalia are similar, though the testes, always mainly pre-ovarial, are far more numerous. Abortipedia indica gen. et sp.nov., from the gills of Caranx hippos, differs from the second species Abortipedia pacifica (Meserve) comb.nov. in details of the clamps, in the lack of oesophageal diverticula, and in its uniquely convoluted ovary. The spines of the lateral genital atrium and penis, and those of the lateral vaginal plaque also, are different, and so are the hosts and geographical locations. Lethacotylinae subfam.nov. has been erected for Lethacotyle Manter & Prince, 1953, in which all the clamps are inhibited, and Bilateracotyle Chauhan, 1945, in which only the anterior pair of the four primary pairs is inhibited. In the latter, the clamps are simple and discocotylid. In both genera, the protohaptor is a large wide hemispherical musculo-glandular organ constricted off from the hind body, and is provided with a plicated cuticle, and bears the three characteristic pairs of anchors; and again in both genera, the posterior-lateral funnel-like organ is particularly prominent. The Protomicrocotyloidea are unique in the higher Monogenoidea in using parts of the body as holdfasts which therefore tend to be substitutes, functionally, for the clamps; they are unique with the doubtful exception of Osphyobothrus Yamag., 1958, in showing a secondary development of the protohaptor.

I would like to thank, sincerely, Miss Nora G. Sproston for maintaining our correspondence and for the exchange of ideas on the present subject and particularly for her collaboration in the last section ‘Relationships of the Protomicrocotyloidea’; Dr N. K. Panikkar for providing facilities for my investigations at the Central Marine Fisheries Research Station, Mandapam Camp, and Dr C. C. John, for permission to collect material from the Marine Biological Laboratory of the University of Kerala, Trivandrum.

The metacercaria of Holostephanus lühei Szidat (1936) is described together with comments on both its linear and tissue distribution within the host (Gasterosteus aculeatus L.), host-parasite reaction and numbers of cysts in relation to the size of the fish.

The adult of Holostephanus lühei Szidat (1936) (syn. H. bursiformis Szidat, 1936) obtained experimentally from the duck and pigeon, is re-described in detail. It is noted that this species is amphitypic and it is suggested that H. dubius (Szidat, 1936) (syn. Cyanocotyloides Dubius, Szidat, 1936) should be reduced to synonymy with H. lühei.

Grateful acknowledgement is expressed to Dr G. Dubois for his interest, advice and valuable opinions given in connexion with this study.

The epidemiology of coccidiosis involving Eimeria perforans, E. media, E. stiedae, E. irresidua, E. magna and E. piriformis was studied for a period of 35 months in a free-living population of wild rabbits, confined to an experimental enclosure.

Relations between the seasonal fluctuations of the above species, on the one hand, and severity of infection and age and social status of hosts, on the other hand, based on the oocyst counts from 2326 faecal samples collected at regular monthly intervals, are indicated.

Mortality within the population was analysed, and coccidiosis was found not to be responsible for the general mortality pattern.

Thanks are due to Mr M. Dudzinski of the Division of Mathematical Statistics, C.S.I.R.O., Canberra for statistical analysis of the data. Mr H. McL. Gordon and Dr J. C. Boray of MacMaster Laboratories, C.S.I.R.O., Sydney, and Dr W. L. Nicholas, of the Australian National University, Canberra, read the manuscript and offered many helpful suggestions. Messrs E. R. Hesterman and D. Purchase of the Wildlife Survey Section, C.S.I.R.O., Canberra, provided valuable technical assistance.

1. The life history of Hymenolepis farciminosa (Goeze), first reported in 1955, has been described.

2. The grasshoppers Acrotylus humbertianus Sauss., Acrida exaltata Walk., Oedaleus abruptus Thunb., Crotogonus sp. and Aiolopus sp. were found, experimentally, to serve as intermediate hosts. The cysticercoid has been described and figured. A crow was experimentally infected with the cysticercoid and the adult tapeworm recovered.

The authors wish to express their gratitude to Mr L. Sahai, M.Sc., M.R.C.V.S., the then Director of the Institute, for providing the requisite facilities, and to Dr H. D. Srivastava, M.Sc., D.Sc., F.N.I., Head of the Division of Parasitology, for valuable advice. They are grateful to Dr B. P. Uvarov, Director, Anti-Locust Research Centre, London, and to Dr A. P. Kapoor of the Zoological Survey of India for the identification of the insects.

The mites known to parasitize the lower respiratory tract of birds are discussed and a host list of the various species is given.

Sternostoma tracheacolum Lawrence, 1948, is redescribed and the variations in specimens from various hosts and localities are analysed. The synonymy of S. castroae with S. tracheacolum is confirmed and S. meddai and Agapornyssus faini are made new synonyms of S. tracheacolum. The specimens found in canaries vary widely according to the origin of the host. Those from South African and Italian canaries are closely related morphologically and present relatively long chelae, while specimens from Belgian and North American canaries have much smaller chelae. An intermediate form is found in a Brazilian canary. S. tracheacolum is thought to use wild birds as its normal hosts since it has been found repeatedly in birds in North America, as well as in other parts of the world, and because its presence in the trachea and lungs in these birds seems to be much better tolerated than in the canaries. Canaries are thus probably infested secondarily, and it seems that Passer domesticus has served in the transfer of the mites between the two groups. The specimens from wild birds present the same variability as those of the canaries, and one can also distinguish three different groups on the basis of the length of the chela. The origin of these variations is discussed. Geographical or biological isolation of the host probably plays a more important role than the host itself in the production of variation.

Hypopi representing probably two species of the genus Falculifer have been found in the air-sacs and lungs of two central African birds. Also Speleognathus poffei, S. striatus and Boydaia sp. have been taken from the lungs or trachea of their hosts in Ruanda-Urundi or U.S.A.

Collection of most North American material was carried out under a research grant (G-11035) from the National Science Foundation.

The authors wish to thank the following for their co-operation and assistance in this study by making available various collections of Sternostoma tracheacolum: E. W. Baker, U.S. National Museum, Washington, D.C.; G. Owen Evans, British Museum (Natural History), London; D. P. Furman, University of California, Berkeley; S. Grétillat, Laboratoire Central de l'Elevage, Dakar; R. F. Lawrence, Natal Museum, Pietermaritzburg; and G. Lombardini, Rome.

1. Seventy-three females, 1 male, 20 nymphs and 1 larva of Ixodes arboricola Schulze & Schlottke, 1929 were found on a juvenile enfeebled starling (June, 1933, Denmark).

2. Range of variability of employed systematic characteristics of this species has been checked, and it was found impossible to preserve the following subspecies of I. arboricola, muscicapae, domesticus and bogatschevi.

3. Between length and breadth of idiosoma of female, and between lengths of legs I and III (excluding trochanter and coxa) the ratio was found to be almost linear. A deformed leg II is described as a case of regeneration.

4. I. arboricola, I. passericola, I. dryadis, and I. strigicola are regarded as synonyms and have all been incorporated in the species I. arboricola, the habitat of which is birds' nests in tree cavities.

For supplying material for this study I wish to thank Professor M. Christiansen, State Veterinary Serum Laboratory, Copenhagen; Dr B. Hubendick, Director of ‘Naturhistoriska Museet’, Gothenburg; Dr S. L. Tuxen, Head of the entomological department of ‘Universitetets zoologiske Museum’, Copenhagen, and Dr Glen M. Kohls, Sanitarian director for the loan of P. Schulze's former collection of ticks.

I am most thankful to Dr Don Arthur, for advice and critical reading of the manuscript.

1. A technique is described for the preparation of axenic cultures of protoscolices of Echinococcus granulosus.

2. Protoscolices removed aseptically from hydatid cysts are treated with 0·02% crystalline pepsin at pH 2·0 for 10 min. at 38°C. in order to remove (a) daughter cyst germinal membranes, and (b) dead or degenerating protoscolices.

3. Protoscolices may be maintained for more than 100 days in a variety of media. These include media containing various proportions of some of the following: chick embryo extract, beef embryo extract, hydatid fluid, bovine amniotic fluid, Parker 199, bovine serum.

4. 10–20 ml. of culture media was used at 38°C., either in roller tubes or shaken in a water-bath. Media were renewed every 48 hr.

5. Protoscolices developed into cysts by two routes, either (a) by becoming vesicular, gradually growing in size, and finally becoming enclosed in a laminated envelope, or (b) by forming a ‘posterior bladder’ which became relatively enormous and ultimately absorbed the scolex region, the whole forming a cyst within an envelope as in (a).

6. In the majority of media, after about 31–48 days' culture, a thin envelope was secreted which developed later into a thick laminated membrane.

7. Cysts with laminated membranes ultimately underwent fatty degeneration and became cytologically abnormal.

8. In the most successful experiments, cells or clusters of cells formed within the cysts and these may have represented the anlagen of the protoscolices.

9. In no case was segmentation, or any other sign of strobilar development, obtained.

10. These results show that the laminated membrane in E. granulosus is initially of parasite origin and not of host origin as believed by some workers to be the case.

11. Since there is evidence from the literature that E. multilocularis does not form such an envelope in vitro, a clear developmental difference appears to exist between the two species.

12. It is suggested that this difference offers an explanation for the formation of unilocular or multilocular cysts. Since E. granulosus secretes a laminated envelope, its development is limited to a single or unilocular type of cyst. In the case of E. multilocularis no such limitation occurs, so that the invasive multilocular type of cyst could more easily develop.

Natural infection with the cephalobid nematode, Daubaylia potomaca, is reported in Helisoma antrosum pericarinatum ( = H. anceps pericarinatum) collected in the vicinity of the University of Michigan Biological Station on Douglas Lake, Cheboygan, Michigan.

The life-cycle of D. potomaca, which appears to be unique, has been determined and reproduced experimentally utilizing Australorbis glabratus and other snails as hosts. The cycle involves escape from the host by gravid females, invasion by the females of new hosts and the reproduction therein of generation after generation of parasites, and the eventual emergence of female worms from dying hosts to the external aquatic environment. The parasite does not lead a saprozoic existence, and no dauer larvae were seen. Except for the newly emerged female, no stage of D. potomaca is ‘free-living’, and there is no evidence that transmission can occur except through the agency of these females. However, parasitic females removed at any time from their hosts by dissection are fully capable of infecting new hosts under experimental conditions.

Dissection of A. glabratus infected with known numbers of female D. potomaca disclosed that the gravid nematodes deposit about two eggs per day in the tissues, that larvae may be found after 5 days of infection, and that the first ‘new’ generation of adult males and females appears within the host 11 or more days after infection. Continued reproduction in the host may give rise to very large nematode populations. A. glabratus exposed to five female D. potomaca usually became infected and all infected snails were killed within 44 days. Death of infected snails was preceded, in nearly every case, by the emergence of female D. potomaca from their hosts. It is suggested that this phenomenon reflects an adaptive response of the worms to changes in the internal milieu of the snail.

Attempts to infect certain physid and lymnaeid snails with D. potomaca failed, and varying degrees of success were achieved in attempts to infect several planorbids. Of the latter, the most suitable hosts appeared to be A. glabratus (Puerto Rico) and Helisoma sp. (Michigan); the least suitable host was Helisoma caribaeum (Puerto Rico and St Croix), in which an intense tissue reaction killed all nematode eggs before they could hatch. Other susceptible planorbids (in declining order of apparent suitability as hosts) were Helisoma trivolvis ? macrostomum (Canada), Bulinus truncatus (Egypt) and Planorbarius corneus (Massachusetts).

Some of the problems associated with the possible use of D. potomaca as a means of biological control for A. glabratus are discussed.

It is a pleasure to thank the persons whose names appear in the text for aid or counsel graciously extended. I am also grateful to Dr George L. Graham (University of Pennsylvania) for certain citations in the literature, to Dr M. R. Tripp (now at the University of Delaware) for receiving the shipments of snails in Boston, and to Dr A. H. Stockard, Director of the University of Michigan Biological Station, for facilitating the field work.

A secretory cycle has been revealed in the intestinal epithelial cells of Fasciola hepatica. The basal regions of tall cells contain mitochondria-like bodies which stain deeply with basic dyes. These granules become numerous and are then arranged in vertical arrays of variable height which extend into the middle region of their cells. The distal halves of the epithelial cells contain numerous granules or droplets which have no affinity for basic stains and tend to swell, with consequent disarray of the secretory products. In the terminal parts of the cells vacuole-like formations appear, usually one to each cell, and eventually the lumen of the caecum becomes occluded by a froth-like mass of vacuoles. When food enters the caecum in small amount, the vacuoles are broken down and some secretion is liberated and mixed with the incoming homogenate. Meanwhile the vacuole-like structures encroach more deeply into the cell and eventually the residual secretion is discharged. New cell boundaries are being established near the nuclear zone and after complete discharge of secretion the distal parts of the cells consist of aggregates of long cytoplasmic filaments, which form a kind of fringe on the free borders of the now much shortened cells. These delicate cytoplasmic fringes, are abraded, probably by the physical action of streams of food, and typical short cells in caeca which contain food have much shorter fringes no more than one-half the height of the shallow cells. Ultimately all traces of such residual cytoplasm remaining after completion of the secretory cycle disappear. Short cells containing few granules are presumed to increase in height subsequently by regeneration of cytoplasm and, possibly, nuclear changes also, until they attain the form seen in cells commencing the secretory cycle. Such changes are especially difficult to observe because of variability in the heights of cells normally forming the epithelium. The especially tall cells which are seen, isolated or in small groups, at the height of the secretory cycle—the so-called pyramidal cells—are believed to be merely cells which have had their secretory activities delayed; ultimately, they are denuded in the same way as other cells during the secretory cycle. The type of secretory activity disclosed is therefore of the apocrine type, which is considered appropriate to the suctorial method of feeding employed by the fluke.

1. The development of resistance to proguanil and pyrimethamine was studied in a clone of Plasmodium gallinaceum (strain A) derived from a single erythrocytic parasite and maintained by a standard method of serial inoculations in young chicks.

2. The rate of the development of resistance to 0·05 mg./20 g. doses of proguanil was compared in strains maintained by inocula of 5 × 107, 108 and 109 parasites. Some evidence was obtained that the rate of the development of resistance to the drug was related to the numbers of parasites in the inocula.

3. No correlation was observed between the rate of the development of resistance to pyrimethamine and the size of the population of parasites exposed to its action in strains treated with 0·001 g./20 g. doses of the drug and maintained by inocula of 5 × 107 parasites or 109 parasites; but a greater variability was observed in the rate in the strains maintained by the small inocula than in the strains maintained by the large inocula. Resistance appeared to develop sporadically.

4. Some evidence was obtained that strains treated with a high dose of pyrimethamine (0·05 mg./20 g.) might become more sensitive to the drug as a result of treatment. In three experiments the infections were eradicated by the second or third course of treatment with the drug. However, strains which withstood this dose, developed resistance as rapidly, or more rapidly than those treated with 0·001 mg./20 g. doses. There was therefore no evidence from these experiments with pyrimethamine that resistance to the drug could be produced more readily with small than with large doses of the drug.

5. Except for slight variations, resistance to proguanil developed concurrently with resistance to pyrimethamine in strains treated with that drug.

6. In many of the strains, whether treated with proguanil or with pyrimethamine, resistance appeared to develop quite suddenly, but in others it developed more gradually. The pattern of the development of resistance in strains treated with either of these drugs could be explained by the selection of spontaneously occurring mutants, though some of the data suggested that the mutants differed in degree of resistance to the drug.

7. The rate of development of resistance to pyrimethamine was studied in strains derived from primary inocula composed of known numbers of pyrimethamine resistant parasites and 5 × 107 parasites of the untreated strain A. The addition of at least 106 resistant parasites to the inoculum was required to produce an increase in parasitaemia during the subsequent course of treatment with the drug, but the addition of 102 resistant parasites or, in some experiments, fewer than 102 resistant parasites to the primary inoculum was sufficient to produce a heavy parasitaemia during the second serial course of treatment if the strain was maintained by the standard method (p. 496). When these results are compared with the pattern of the development of resistance to pyrimethamine in the strains treated with that drug, it can be concluded that only in one strain was there any evidence that resistant parasites were present in the primary inoculum when it consisted only of parasites of the untreated parent strain. The rate of development of resistance in many of the strains treated with either proguanil or pyrimethamine suggested a mutation rate of a low frequency.

1. The ecological relationships and life history of a Diplostomulum type of strigeid metacercaria encountered in several fresh-water fishes of Andhra Pradesh are described.

2. The development of the adult strigeid in the pond heron and cattle egret and structure and development of the miracidium have been traced.

3. The adult individuals are identical with Diplostomum ketupanensis Vidyarthi, 1937. It is suggested that D. heronei described by Srivastava (1954) may be a synonym of D. ketupanensis.

4. Attention is drawn to the possible relationship between D. heronei and the metacercaria Diplostomulum pigmentata Singh, 1956, which in its turn appears to be similar to the Diplostomulum in the present study.

We thank Sri S. Nagaraja Rao of Fisheries Department, Andhra Pradesh, for his kind help and co-operation.

Eperythrozoon teganodes is described from the blood of cattle. It is compared with, and is shown to be distinct from, E. wenyoni Adler & Ellenbogen, 1934. E. teganodes is a parasite of the plasma rather than of the erythrocyte. It occurs as fine rods and threads, rings, and rings with a rod or thread attached. (E. wenyoni adheres to the edge and the face of the erythrocyte, appearing as densely staining coccoids and faintly staining disks.) It is suggested that some highly polymorphic species of Eperythrozoon may prove to be a mixture of two or more species.

I wish to thank Professor J. F. A. Sprent for his advice and for criticizing the manuscript, and Messrs J. Ballantyne, C. Boel and F. Mellis for technical assistance. The photographs were taken by Mr E. Hollywood of the Photographic Department of the University of Queensland. I am grateful to Dr D. W. Brocklesby for allowing me to examine his material. This work was aided by facilities and funds provided by the Rural Credits Fund of the Reserve Bank of Australia, and by the Queensland Dairymen's Organization.

1. Leucine aminopeptidase has been detected, histochemically, in the intestine, in the walls of the anterior part of the excretory canals and in the hypodermis of Ascaris lumbricoides.

2. The possible significance of leucine aminopeptidase in the walls of the excretory canal is discussed.

I wish to thank Dr Tate, in whose department this work was carried out, for his advice and encouragement during this investigation and Mr A. Page for technical assistance.

In a paper recently published (Lee, 1961) I described as new two species of freshwater nematodes. Since that paper was published my attention has been drawn to papers by Andrassy (1959, 1960) and Meyl (1957) and to the fact that I did not give a differential diagnosis, without which the specific names are not valid. The keys given by Thorne & Swanger (1936) and by Thorne (1939) were used initially to try to identify the specimens, which were compared with various species recorded up to 1956 in the Zoological Record. They have since been re-examined in the light of Andrassy's papers, (1959, 1960) and Meyl's (1957). Re-examination of the specimens showed that the guiding ring of Dorylaimus keilini is double (Fig. 1) and not single, as was originally figured (Lee, 1961).