Anthobothrium auriculatum (Rud.) is often referred to as ‘an insufficiently known species’. Southwell (1925) states that ‘all that is known about this doubtful species is contained in Rudolphi's brief description, which is quite insufficient to diagnose the species with, certainty’. Rudolphi (1819) first described it as Bothriocephalus auriculatus from Torpedo marmorata Risso; it is possible that this brief and inadequate description included several species. Leuckart (1820) described what has since been regarded as the same species under the name of Bothriocephalus flos from Carcharinus glaucus (L.), Bremser (1824) gave a brief account of Bothriocephalus auriculatus, and Zschokke (1888) gave a somewhat fuller account of Anthobothrium Auriculatum from Torpedo marmorata. As far as can be judged all these forms are synonymous. Diesing (1850) described what he thought to be Rudolphi's species, placing it in the genus Tetrabothrium; he obtained it from Torpedo marmorata Risso, Hexanchus griseus (Gm.), Carcharinus glaucus (L.), Squatina squatina (L.), and Raja calvata L. It has been pointed out by several writers that Diesing's Tetrabothrium auriculatum does not agree with Anthobothrium Auriculatum (Rud.), because, among other things, the genital pores in the former are anterior and in the latter posterior. Southwell (1925) states that Beauchamp is of the opinion that Tetrabothrium auriculatum Dies, is synonymous with Phyllobothrium gracile Wedl., an idea which is now generally accepted. Joyeux & Baer (1936) recorded Anthobothrium Auriculatum (Rud.) fairly frequently in a number of host fishes, namely, Mustelus mustelus (L.), Scyliorhinus caniculus (L.), Lamna cornubica (Gm.), Eugaleus galeus (L.), Squatina squatina (L.), Carcharias glaucus (L.), Torpedo marmorata Risso, and Raja clavata L. They, too, refer to the species as imperfectly known, and suggest that it might be synonymous with some other species of the same genus. In view of the lack of an adequate description of Anthobothrium Auriculatum it was felt that an account of its anatomy would render future identification of the species simpler and would settle the question as to whether or not it was synonymous with some other known species.

It has been known for a long time that certain species of Mallophaga attach themselves to hippoboscid flies, the act taking place on the bird host. This has been referred to as Phoresy, ‘a type of interrelationship between insects in which one is carried on the body of another larger insect, but the former does not feed on the latter’, or, in other words, free passage without food.

Females of Littorina obesa, L. scabra and L. littorea have been shown by other workers to grow more rapidly than the males so that they predominate in the larger size groups. They are significantly more numerous than the males among the larger specimens of L. neritoides on the Plymouth Breakwater.

More male than female snails are infected by a larval trematode, Metacercaria A, when it occurs alone, and the percentage infection falls when the proportion of males falls. A second larval trematode, Cercaria B, infects more female snails than males. Infections with this species alone remain consistently low, but where it occurs in the same snails as Metacercaria A the percentage infection rises rapidly, that is, in the larger size groups of the snails where the females predominate. Females infected by Cercaria B appear then to be attractive to the metacercariae.

Evidence is given to show that it is extremely unlikely that these large female snails were originally males in which sex reversal has occurred.

This different intensity of infection of the sexes of L. neritoides is considered to be primarily responsible for the shapes of the curves when infection is plotted against size, and it does not appear likely that primary infections with larval trematodes cause acceleration of the growth rate in this species.

It is thought that ecological factors on the breakwater are likely to be the chief causes of the large size attained there by L. neritoides.

During the examination of over 8000 specimens of Ornithodorus moubata, two cases of partial twinning (one male, one female) of the posterior region were noticed, and also a case of suppression of the postanal region in a male. All the freaks were viable, and the partial twins were normally fertile.

The larval stages of the celery fly, Acidia heraclei, have been described, and it is shown that this larva agrees with other biontophagous dipterous larvae in having the pharynx devoid of ventral ridges. The transparency of the larvae permits the internal anatomy to be seen clearly in the living larva, and by this means the structure of the perispiracular glands is clearly revealed.

The braconid Adelura apii occurs as a parasite of Acidia heraclei larvae, and its first. stage larva is described in detail. This larva is densely hairy, has a long, curved, hairy, tail-like appendage and, by the more rapid growth of the ventral surface, it develops a dorsal curvature which obscures the true orientation so that the true dorsal surface appears externally to be ventral. In these respects the first stage larva of Adelura apii resembles that of A. gahani described by de la Baume-Pluvinel. The later larval stages of A. apii, of which there are at least two, are naked, lack the tail-like appendage and do not differ from the normal type of parasitic hymenopterous larvae.

A yeast-like fungus occurs as a parasite in the blood of Acidia heraclei larvae. It is always found associated with existing or abortive infection of the larvae with Adelura apii. Dense mycelial masses sometimes occur in the gut of A. apii pupae and are probably derived from the yeast cells parasitic in the host larvae. It is suggested that this is a unique case of a fungus parasitic in a host larva (Acidia heraclei) undergoing part of its development in a parasitic braconid (Adelura apii), adult females of which transmit the fungus to the host larva during oviposition.

The larva of Phaonia palpata closely resembles that of P. variegata in the structure of the buccopharyngeal armature and of the posterior spiracles. The absence of sharp teeth on the anterior ribbons and the presence of a blunt knob on the ventral edge of the oral bars distinguish the larva of P. palpata from larvae of other species of Phaonia.

1. The anatomy of three digenetic trematodes from Conger conger (Linn.), Skrjabiniella aculeatus (Odhner), Lecithochirium rufoviride (Rud.) and Sterrhurus fusiformis (Luhe) has been described. The technique employed is given, and in each case the history of the species has been traced.

2. The discussion on the nomenclature of Skrjabiniella aculeatus explains why this generic name used by Issaitschikow (1928) has been adopted in this work in place of Prosorhynchus, and a key to the genera Prosorhynchus s.str. and Skrjabiniella has been suggested. A table showing the proposed division of Odhner's genus Prosorhynchus is included.

3. In the discussion on the hemiurid worms it is pointed out that there is no sound basis for the separation of the genera Lecithochirium and Sterrhurus as they stand.

During my work on the mites I have often wished that a book were available in which all the known and valid genera and species of parasitic mites could be found. The literature on the Acarina contains numerous genera and species which are synonyms of older identifications.

Huff & Gambrell (1934), and Gambrell (1937) observed that, when Plasmodium cathemerium was passaged from canary to canary for a long period, by inoculation of blood from acutely infected birds, the number of gametocytes produced in each infection gradually decreased, though in two strains only did they disappear completely.