The material which forms the basis of the following account consists of two tubes of tapeworms collected from ostriches at the Veterinary Pathological Laboratory, Nairobi, British East Africa. One tube contained approximately 12 scolices and the anterior portions of the strobilae attached to them, together with several fragments of the more posterior portions: these are described under the name Davainea beddardi n. sp. The other tube contained one large fragment of a Davainea and several smaller pieces but no scolices: these are described under the heading Davainea sp. For this material I am indebted to Professor G. H. F. Nuttall, F.R.S. to whom I wish here to express my thanks. I have also to acknowledge my indebtedness to the Librarian of the Royal College of Veterinary Surgeons for allowing me to consult literature unobtainable elsewhere.

Whilst working through the collections of Nematodes at the Punjab Veterinary College in Lahore I had the opportunity of examining a number of Strongylid worms from the Indian camel (Camelus dromedarius) belonging to two species, labelled Haemonchus longistipes and Nematodirus spathiger, respectively.

The usual host of this new parasite, Helicosporidium parasiticum, is the larva of a Ceratopogonid, Dasyhelea obscura Winnertz, which lives in the decomposed sap filling the wounds of trees—elm and horse-chestnut. All the material used for this study was derived from the wounds of two trees only: (1) an elm tree standing on the Caius College ground at Newnham, facing Church Rate Walk, and (2) a horse-chestnut standing between the School of Agriculture and Downing College.

The material of the species to be described was found in a small collection of parasites from Zanzibar, placed at my disposal by Professor G. H. F. Nuttall, F.R.S., to whom I wish to express my thanks. As only a few cestodes have hitherto been recorded from East Africa and its helminth fauna is therefore largely unknown, a list of the forms identified is given at the end of the paper. I desire to acknowledge my indebtedness to the Birmingham Natural History and Philosophical Society for a grant towards the expense of preparing the plates, both in this and the preceding paper (Parasitology, XIII. No. 1, March 1921, p. 1).

In the paper on the association of Rickettsia with Trench Fever, by Arkwright, Bacot and Duncan (1919) mention is made of a bacillary infection of the excreta and guts of lice (Pediculus humcmus). A Gram-negative cocco-bacillus was isolated in pure culture. It was non-motile, fermented glucose, mannite and lactose very slowly, and formed acid and clot in milk in about 14 days.

Warburton (1920) has recently published a survey of our present knowledge of the mites of the genus Sarcoptes; from his survey it is clear that in spite of all the work that has been done upon these mites, much of it by most pains-taking anatomists, we are still without an accurate knowledge of the anatomy of any one species of Sarcoptes. This is, in part at any rate, due to the fact that some of the best work was done, by Robin and others, between 1860 and 1865, at a time when microscopes and technique were by no means as highly developed as they now are.

1. Cercaria pekinensis, a new cystocercous cercaria, is described.

2. The excretory system of the developed cercaria consists of a bladder, a drainage channel through the tail and a pair of anterior collecting tubules, each of which receives eight main (tertiary) branches. Each branch is composed of 2 × 4 × 4 units. The posterior-most branch cares for the drainage of the tail, including the corresponding flapper.

3. A study of representative stages in development shows that the common denominator of the excretory system is α + β, while the pattern of the developed cercaria is expressed by 4 (α)2 + 4 (β)2.

4. The fundamental pattern of tie cercaria is likewise found in the sporocyst.

5. These data have a significant bearing on the application of mathematics to the problems of growth and development.

Although some of the earliest work on the Strongylid parasites of horses was done by Giles in India in 1892, the subject has been almost completely neglected in this country since that date; even the comparatively recent list of Indian parasites compiled by Gaiger (1910) makes no attempt to differentiate the numerous Nematodes which had been confused under the names Sclerostomum equinum and S. tetracanthum until the appearance of Looss' famous monograph in 1902.

A Batch of twenty-nine larvae of Stegomyia scutellaris Walker, were collected on 24 July 1920 from an old earthenware pot found in a Malay's garden. It was at once seen, even with the unaided eye, that many, some considerably paler than others, were characterised by a pearly-white opalescence of the tracheal gills at the hinder end of the body.

Our knowledge of the systematics of the genus Sarcoptes is in an unsatisfactory state. About a score of species have been admitted, many of which have never been seen since they were described. Many of the descriptions date from between sixty and seventy years ago, a period when microscopes and microscopical technique were barely adequate to cope with so difficult a genus as Sarcoptes is. In order to provide a basis for further study of Sarcoptes, Warburton (1920) published a critical survey of our knowledge regarding these mites. His review of the literature has proved invaluable to myself, and is the foundation on which I have worked. In the foregoing paper (pp. 114–145) I published an only too lengthy description of the Sarcoptes of the horse, finding that a full description of one form was necessary as a basis for comparison. Since we do not know what anatomical points are of systematic importance, attention was given to all details of the external anatomy.

The forms under consideration resemble Rickettsia prowazeki—the supposed cause of typhus fever—which occurs in lice that have fed on typhus fever patients.

1. Copulation between individuals of the two species O. moubata, and O. savignyi may occur, and the stimulus of coition may induce oviposition, the eggs being non-fertile.

2. There is no evidence of parthenogenesis in this species, nor do these ticks undergo ecdysis after reaching maturity.

3. An increase in temperature of 8° C. from 22° C. (a) doubles the.rate of oviposition, (b) decreases the fertility of the eggs by 30 per cent., (c) reduces the longevity of the female tick from 715 to 397 days, i.e. by 40 per cent, and (d) approximately halves the period required for metamorphosis, under laboratory conditions. Under these conditions at 37° C., reproduction is inhibited, and the longevity of the female is reduced by 80 per cent.

4. An individual may undergo from four to eight ecdyses before reaching maturity, the great majority of the males appearing after the fifth ecdysis and the females about equally after the fifth and sixth ecdyses.

5. Engorgement can take place one or two days after emergence, at any stage, the average time required being three-quarters of an hour. There is great variation in the extent of engorgement at each stage, but this is not correlated with the ecdysis period. The largest meal may be taken either before or after an individual reaches maturity.

6. Moisture has an adverse influence on the vitality of the individual, excess of moisture inhibiting growth.

7. An approximation to the stage of development attained can be made after the study of the structure of the hypostome, leg and spiracle. The larval and first four nymphal stages are fairly well differentiated, much more so than the later stages, but variation due to nutrition requires further study.

The material which forms the subject of this communication was derived from Dr W. A. Lamborn's collection, and was placed at my disposal through the kindness of Dr Guy A. K. Marshall, Director of the Imperial Bureau of Entomology, London. It comprised eight larvae of Stegomyia scutellaris Walker, which had been preserved in formaldehyde solution (10 per cent.), and the specimens were mounted individually on microscope slides in the same medium.

It is a common experience that mosquito larvae when they are brought into a laboratory to undergo their development, often fail to develop normally. At times a high mortality takes place, or the larvae lapse into a condition of suspended development continuing as larvae for months. The latter phase usually ends in death before pupation can take place. I have been puzzled to account for these manifestations for a very long time, and have conducted various experiments in the hope of discovering the cause. The general opinion on the matter, I think, is that there is “something wrong with the food supply,” but as a matter of fact larvae supplied with an ample diet often show the same state of affairs.

Among the recent advances in our knowledge of the aetiology of human diseases, one of the most interesting is the discovery of a new group of somewhat problematic organisms which have been grouped together under the generic name Rickettsia. Up to now their presence has been shown, more or less satisfactorily, to be associated with three types of human fevers, viz. typhus, trench fever and possibly Rocky Mountain spotted fever, and in the last few years a certain number of papers have appeared on this subject, the most comprehensive of which are those published by the British War Office Committee and the American Commission on trench fever. In addition it has been suggested that many other human diseases are caused by these organisms, but the evidence is so very unsatisfactory that it may be disregarded.

Since the publication of Part IV (Stewart, 1919), four papers dealing with the life-history of Ascaris lumbricoides have appeared.

(1) Ransom and Foster (1920) give a full account of their work, preliminary reports of which have already been published (1917 and 1919).

As evidence in the problem of whether the worm can undergo full development in one host alone, they attach great importance to two experiments, one on a kid and one on a lamb, in which after the administration of ripe eggs of A. suilla, they recovered worms from the intestines. In the kid, which died 24 days after the first feeding, the worms measured from 4·3 to 11·4 mm.; in the lamb, which was killed 103 days after feeding, the worms measured from 60 to 110 mm. The authors consider that, as Ascaris infection is uncommon in goats and sheep, the worms may without doubt be ascribed to the experimental feeding. They record five experiments on pigs which gave doubtful results, since the pigs fed with Ascaris eggs were found, after varying periods, to be on the average less infected with Ascaris than pigs which were kept as controls, and had not been so fed.

A consideration of the above experiments, and of the available literature dealing with the distribution of trypanosomes and tsetse flies in nature, has suggested certain general conclusions which will now be put forward.

Among six parasitised larve of Stegomya scutellaris Walker, collected by Dr W. A. Lamborn in the Federated Malay States, Five Contained a ciliate which I have described(Parasitology, XIII. p.216)under the name of Lambornella stegomyiae n.g., n.sp., while the remaining larva harboured a new parasitic fungus which forms the subject of this communication. The larva had been fixed and was preserved in formaldehyde solution (10 per cent.) and was labelled: “Larva of Stegomyia scutellaris Walker. Infestation with protozoal parasite and a luxuriant growth of Vorticella. Kajang,” by Dr Lamborn. When the larva was examined under a low power the surface of its body was found to be extensively covered with tufts of Vorticella, whilst its interior harboured an enormous number of parasites which in the gills and the posterior segments were packed in solid masses completely filling these parts (Fig. 1). As seen by transparency the parasites are oval in shape, 37·5 to 57 μ long and 20 to 30 μ in diameter, surrounded by a more or less thick yellowish wall. In their external appearance, size, and position in the host, they are so surprisingly similar to Lambornella that it was at first quite natural to take them for the resting stages or cysts of this ciliate.

There are three species of true parasites in the genus Aphelenchus, viz.: A. fragariae R.B., 1891, A. olesistus R.B., 1893, and A. phyllophagus n.sp. A. ormerodis R.B., 1891, is a doubtful species, possibly a young form of A. fragariae (Marcinowski, 1908).

A. fragariae causes the disease strawberry bunch; A. olesistus and phyllophagus cause leaf disease in flowering plants and ferns. The diseases are widely distributed and of considerable economic importance.

From the study of the anatomy of the three species certain points of general importance emerge: (1) The salivary glands of Aphelenchus represent the oesophageal glands of other nematode genera, which have separated from the body of the oesophagus. This separation causes the reduction in size of the posterior portion of the oesophagus, and its lack of clear demarcation from the intestine. (2) The excretory organ of Aphelenchus, and of some other nematode genera, originates from the left lateral line. (3) The vaginae are ectodermal organs distinct in origin from the gonads proper.

The life cycle of the parasitic Aphelenchi is divided into three definite stages: (A) That of residence in the definitive habitat, which for A. fragariae is in the stem and leaves of the strawberry plant, for A. olesistus and phyllophagus in the mesophyll spaces of the leaves of many plants. Nutrition and reproduction are most actively carried on in this situation, several or many generations succeeding each other, and here the pathological effects are manifest. (B) The resting stage in the soil. The worms reach the soil in fallen leaves, and the adults survive in a partially dried, dormant condition on the surface of the soil for prolonged periods. (C) The stage of immigration into the host plant. When revived by moisture the Aphelenchi may be attracted by a suitable plant, and wanders on to it; they may live as ectoparasites in the leaf axils, breeding in this situation, the larvae migrating to the definitive habitat; or they may enter the definitive habitat direct. They do not traverse the tissues of the stem during immigration. A. olesistus and phyllophagus enter the mesophyll spaces through the stomata.

It should be noted that this life cycle is that of the race, not of the individual. It comprises many generations, and in this respect resembles that of Tylenchus dipsaci and differs from that of T. tritici, which includes one generation only.

In the life of the individual Aphelenchus, embryonic development occupies not more than five days, embryonic and larval development not more than ten, and a complete generation not more than fourteen days.

High atmospheric humidity assists the migration of the worms, previous disease or injury of the host plant may do so. Some races of various species of plants are immune.

Treatment of the affected plants by chemical methods is of limited applicability. Treatment by immersion in water at 50–52° C. for five minutes is recommended by Marcinowski (1908). Prophylaxis should be based on burning of infected plants and leaves, and on the avoidance of infected surface soil in the filling of pots and boxes.

1. The specimens in the material here dealt with make a series of forms connecting F. angusta (Railliet) and F. aegyptiaca (Looss).

2. No important character separates any of these flukes from F. gigantica (Cobbold) and they must accordingly be all identified with this species.

3. The following key represents the simplest method of distinguishing between the species of Fasciola at present described. (For detailed diagnoses see the literature referred to below and this paper.)