1. This paper comprises a study of the larval morphology and biology of the dipterous parasites of the terrestrial Isopods or woodlice.

2. Porcellio scaber L., Oniscus asellus L., Metaponorthus pruinosus Brandt., and Armadillidium vulgare Lat., were found to be attacked by one or more of the parasites.

3. Seven dipterous parasites have been reared and identified from woodlice: Plesina maculata Fall., Melanophora roralis L., Phyto melanocephala Meig., Styloneuria discrepans Pand., Frauenfeldia rubricosa Meig., Cyrillia angustifrons Rond., and Rhinophora lepida Meig. The biology and larval forms of all of these except R. lepida are described and figured, together with those of two undetermined species, “A” and “B.”

A preliminary survey of parasites from Apodemus hebridensis, Mus musculus and Epimys norvegicus on the Isle of Lewis, Outer Hebrides, is described; also the fauna of House Mouse nests. Special discussion is given of the flea fauna, and it is shown that there is much overlapping in host relations. The original flea fauna of Apodemus on the outer islands of the British Isles is indicated.

It will be convenient at this point, before proceeding to a more general discussion of the findings, to summarize all the experiments recorded in the eight preceding subsections. Briefly the results are as follows:

(i) An attempt to infect a Macacus rhesus by feeding it with Trichomonas isolated from a monkey of the same species failed completely.

(ii) Four similar attempts to infect a Macacus sinicus with the same Trichomonas (from M. rhesus) were equally unsuccessful.

(iii) Two attempts to infect another M. sinicus by intra-intestinal inoculation with the same flagellate were likewise wholly negative.

(iv) One attempt to infect a man per os with the same strain of Trichomonas (from M. rhesus) did not succeed.

(v) A strain of Trichomonas from Man, when fed to a Macacus rhesus, produced no infection.

(vi) The same strain (T. hominis) fed to a Macacus sinicus likewise failed to infect.

(vii) A strain of Trichomonas from Macacus nemestrinus, however, when fed to M. rhesus, gave rise to a temporary infection lasting about a month.

(viii) This Trichomonas (from M. nemestrinus, after passage through M. rhesus) produced, nevertheless, a permanent infection—lasting 4½ years to date—when fed to a man.

(ix) The same strain of Trichomonas (from M. nemestrinus), after passage through M. rhesus and Man, when fed to a Macacus sinicus gave rise to an infection which endured for approximately 1½ months and then died out. But

(x) The very same Trichomonas (which was derived from M. nemestrinus, and which produced a temporary intestinal infection in M. rhesus and M. sinicus, and a permanent intestinal infection in Man) when introduced into the vagina of M. sinicus established itself enduringly as a typical “T. vaginalis.” The infection has now persisted for ome 3⅓ years.

(xi) The monkey (M. sinicus) in which a permanent vaginal infection with an intestinal Trichtomonas was established, has probably since reacquired no permanent intestinal infection—despite every natural opportunity for such reinfection.

(xii) No macaque suffered any harm whatsoever as a result of inoculation with any strain of Trichomonas–whether successful or unsuccessful.

(xiii) The one man successfully infected with Trichomonas (from M. nemestrinus) has likewise remained normal ever since.

In theory, a parasite whose effective reproductive rate remains, under practically all conditions, equal to, or greater than, the effective reproductive rate of its host, ought eventually to annihilate it, or, at least, to produce an abrupt reduction in the host population, so great, that it is almost impossible for the vast majority of the emerging parasites to find any prey; so that the parasite population suffers, in its turn, an abrupt and catastrophic reduction, after which the host again increases, followed in due course by the parasite. The numerical fluctuations occurring as a result of this interaction, under various conditions, have been the subject of much theoretical study, but relatively little is known about what really happens in nature. The following brief account of the development of a colony of the Chalcid parasite, Aphelinus mali Hald., at the expense of its host, Eriosoma lanigerum Hausm., may therefore be of interest.

The following is supplementary to the previous lists (Leigh-Sharpe, 1926 and 1933), and consists of records of parasitic Copepoda taken by workers in that group who have visited the Laboratory of the Marine Biological Association, Plymouth, during 1933.

Flagellates belonging to four genera, Trichomonas, Giardia, Chilomastix, and Retortamonas, have been found in the caecum and colic loops of the muskrat, Fiber (= Ondatra) zibethica.

A Retortamonas is described from the caecum of two laboratory guinea-pigs.

No Worker on British Turbellaria having hitherto given any attention to parasitic species, I devoted the greater part of my visit to the Laboratory of the Marine Biological Association, Plymouth, Aug.–Sept. 1933, to the collection and investigation of these forms. The number discovered is small in proportion to the number of hosts examined. All but the last have been identified from von Graaf (1913), and all but the first and last are new to the British fauna.

The main object of this paper is the description of the larva of a new species of Cecidomyid, found by me in January 1933 in two old beehives from Selehurst, Horsham, Sussex. The adult Cecidomyids, reared from these larvae, were submitted to Dr H. F. Barnes, who has found them to be a new species described by him under the name of Lestodiplosis alvei, in the paper which immediately follows.

Male. Length about 1·5 mm. Antennae slightly longer than head, thorax and abdomen: 2 + 12, basal enlargement of flagellar segments with regular ring of moderately long stout setae and one ring of circumfila, distal enlargement with two rings of circumfila and irregular ring of stout setae, loops of circumfila regular and moderately long, those on basal enlargement extending about one-third length of stem, distal ring on distal enlargement extending about two-thirds length of neck; 1st and 2nd flagellar segments fused; 3rd flagellar segment with stem about three times as long as broad, neck slightly longer, about three-and-a-half times as long as broad, distal end slightly darkened as on all flagellar segments; 10th flagellar segment with stem about four times as long as broad, neck slightly longer in proportion. Palpi quadriarticulate with few setae: proximal segment quadrate, 2nd just over three times as long as broad, 3rd about three times as long as broad, the same width as 2nd, distal segment about four times as long as broad, slightly narrower than two previous segments. Thorax brown. Wings hyaline; 3rd vein reaching margin at apex of wing. Legs hairy; claws moderately curved, simple; empodium slightly shorter than claws. Genitalia: basal clasp segment long narrow, small basal lobe prominent; distal clasp segment long narrow, darkened; dorsal lamella moderate length and breadth, distinctly longer than ventral lamella, deeply emarginate, each lobe rounded; ventral lamella comparatively short but broad; style long, moderately stout.

While studying a collection of roundworm parasites from animals dying in the Philadelphia Zoological Garden, accounts of which appeared in 1929 and 1931, I found ten flukes in it, one of which proved to be new. Two common distomes in the lot, Renifer ellipticus Pratt 1903 and Opisthorchis tenuicollis (Rud. 1819) are from new hosts; the former from an American beaver (Castor canadensis) and the latter from a Canadian lynx (Felis canadensis). The one rare monostome found in the lot is recognised as a new species of the genus Allopyge Johnston 1913 in the family Cyclocoelidae and is named Allopyge undulatus n.sp. It was found in the thoracic air sacs of Lilford's crane (Megalornis grus lilfordi).

1. Coitocaecum anaspidis sp.nov. is a Trematode which exhibits precocious genital activity whilst encysted as a metacercaria in the Tasmanian Mountain Shrimp, Anaspides tasmaniae Thomson.

2. Eggs are laid by the Trematode whilst in the encysted condition, and in some cases the eggs hatch in the cyst giving rise to miracidia which swim freely in the contained fluids.

3. Two hundred specimens of Anaspides tasmaniae were examined and one hundred and twenty-seven found to contain the encysted Trematode.

4. A systematic description of the Trematode is given.

In this paper short descriptions are given of three new species (two Cestodes and a Nematode) contained in a collection kindly entrusted to the writer by Prof. G. H. F. Nuttall, F.R.S., for determination. The material was collected in Queensland by Mr F. H. S. Roberts, and forwarded to Prof. Nuttall by Mr Robert Veitch, Chief Entomologist, Department of Agriculture and Stock, Brisbane.

The genus Petasiger which belongs to the family Echinostomidae was proposed by Dietz in 1909, with Petasiger exaeretus as the type species. The description given by Dietz of this species is incomplete and it is proposed therefore to present below a more detailed account of the anatomy, based on an examination of whole mounts and serial sections. The material was obtained from the small intestine of cormorants shot on the coast of Cardigan Bay between Aberystwyth and Llanrhystyd. Five cormorants were shot in July, and of these two contained a large number of Petasiger exaeretus in the small intestine.