A Preliminary outline of the life history of the lungworm of the cat and its confusion with that of Ollulanus tricuspis, has been given in a previous paper. Since that paper was published, the name of the family of lungworms has been changed to Protostrongylidæ by Professor Leiper; and an examination of adults of the lungworm from the cat, shewed that it belonged to a different genus from the type of the old genus Synthetocaulus. To this new genus, the name ælurostrongylus has been given.

Until recently, it had generally been accepted that the life history of Ollulanus tricuspis was a complicated one involving an intermediate host, the mouse. Last year, however, I drew attention to the fact that the larval stages, both in the cat and in the mouse, believed by Leuckart to belong to Ollulanus, were really those of Ælurostrongylus, the lungworm of the cat. Subsequent work has enabled some of the details of the life history of Ollulanus to be elucidated—although by no means all—and these are considered in this paper.

A Considerable number of specimens of this parasite were collected from the small intestine of a genette which died in the Gardens of the Zoological Society of London.

The cuticle of the cephalic extremity is dilated anteriorly. This swelling is terminated posteriorly by the cuticle incurving to meet a raised ring on the body-wall, about the level of the junction of the anterior and second fifths of the œsophagus. There are no cervical papillæ present, and it is probable that this ring may be regarded as replacing them. Just anterior to the middle of the œsophageal region and at the level of the excretory pore is a cervical groove which completely encircles the body. Laterally the cuticle on the anterior margin is thickened; it is also thickened on the ventral side, but less so than laterally. These thickenings are reinforced by a granular inclusion in the cuticle. The posterior margin is thickened only in the region of the excretory pore.

The classification of the Trematode family Opisthorchiidæ presents some difficulties to the systematist. These difficulties arise partly from the fact that a number of the existing species appear to lack any real morphological characters by which they can be differentiated, slight variations in measurements, together with a difference in host, having been considered sufficient to justify the making of new species. This view has resulted in the placing of undue importance on somewhat minor differences when they do occur in other species, such differences being considered sufficient for creating new genera.

The systematist is further confronted with the difficulty of forming definite opinions on the systematic position of some of the species made by earlier workers. Their descriptions and figures are often inadequate owing to the fact that characters which, in the past, were considered of minor importance are now given much closer attention. Examples of the confusion which has arisen from such a position will be referred to in this paper.

This description of a new species of Paraspidodera is based on material from the Helminthological collection of the London School of Hygiene and Tropical Medicine which was handed to the writer for examination by Professor R. T. Leiper, F.R.S. The parasite had been collected by Dr. Sells from the wild pig in Uganda; no indication of the habitat is given. The writer wishes to thank Professor Leiper for placing this material at his disposal.

Of the various groups of Helminths, Acanthocephala has received the least attention from Helminthologists; so much so that even its classification is based on very arbitrary characters. This may partly be due to the general belief that infestation with these worms is very rare. The earlier accounts, such as that of Diesing (1851), which deals with a number of species from fishes, giving brief descriptions of their external morphology and a few generalised drawings, describe the various species under a single genus, Echinorhynchus.