76 MR. H. CHARLTON BASTIAN'S MONOGRAPH 



in general. Since, however, tlie announcement of the discovery of so many free Nema- 

 toids is likely to suggest to the minds of many the belief that these are identical with 

 the parasites, being merely the revelation of another stage of their life-history, which 

 has hitherto been hidden from us, it seems desirable to bring forward some evidence to 

 disprove such a supposition, and establish the claim of these minute creatures to a distinct 

 and independent place in the animal kingdom — and more especially so since precisely 

 such a view has been taken l)y one of the principal writers on these free Nematodes. For, 

 at the conclusion of his paper before mentioned, Carter, spealdng of the uncertainty still 

 existing with regard to the early history of the Dracnnculiis, adds, " It remains a sub- 

 ject for future and interesting inquiry, but not more so than the still further elucidation 

 of the rilaridte generally, both free and parasitic ; for when we consider that the former 

 abound in species, and are spread in myi-iads probably all over the world, where there is 

 vegetable matter for them to feed upon, in salt as well as in fresh water, in the sea and 

 on the land, while the latter inhabit all animals, perhaps, more or less, down to the 

 lowest worms; that many of the former' leave their habitat and vegetable food for a 

 temporary residence in animals, to live thus on animal food, and that therefore the whole 

 of the parasitic forms may lie orlginalhj derived from the free ones " ; for these, and other 

 reasons, he says, " these worms, at first apparently insignificant from their thread-like 

 form and scarcity, are seen to assume an importance in organic creation which calls for 

 a much more extended study of them than they have as yet received " (p. 112). 



With the view of investigating this question, I made a careful analysis of the anato- 

 mical details and plates given by Dujardin, in his ' Ilistoire naturelle des Helminthes,' 

 of the Nematoid Entozoa, — selecting this writer, not only on account of the more com- 

 plete descriptions found in his work, but also in deference to his extensive practical 

 acquaintance with this particular branch of his subject. The result of this examination 

 has sufl&ced to convince me that the nearly constant combination of several important 

 characters — so universal as to be typical of these free Nematodes — are only probably 

 present in two or perhaps three of the parasitic genera. These distinct characters are 

 furnished by the male and female genital organs, — the males having two equal sub- 

 terminal intromittent spicules, with or Avithout accessory pieces, whilst the females have 

 the vulva situated at about the middle of the body, a short vagina, with a symmetrical 

 double uterus, whose branches lie on opposite sides and are connected with a short and 

 simple reflexed ovarian tube — the only exception to this arrangement being in a few 

 genera, in which, the females having the vulva situated some way behind the middle of 

 the body (about the commencement of the posterior third), the hinder segment of the 

 uterus remains abortive and undeveloped (PI. X. fig. 113), whilst the anterior segment 

 retains its characteristic form. 



On referring to Dujardin's classification", it will be seen that he has ranged the Ne- 

 matoids into seven sections, together with an appendix containing the little-known or 

 anomalous forms. The anatomy of the animals included in his first section, comprising 

 the genera Trichocephalus and Trichosoma, is totally distinct as regards the arrangement 



' Not strictly speaking Neinatoids ; the animals referred to, constituting the genera Gordius and Mcrmis, be'ong 

 in reality to a uearlv allied orJcr, Gordiacea. — H. C. B. - Loc. cit. p. 2. 



