78 MR. H. CHARLTON BASTIAN'S MONOGRAPH 



leading heliniutliologists of the present day, who are almost all now disposed to believe 

 that the parasitic Nematoids exist in an asexual condition within the body of an inter- 

 mediate host, before host and guest are swallowed by those animals destined to harbour 

 the sexually mature Entozoa — the conditions essential to their development seeming to 

 necessitate this intermediate state, instead of that direct and continuous method of evolu- 

 tion from the egg to the adult animal which I have recognized in all the free Nema- 

 todes in their various habitats. Our knowledge of the life-history of the parasites is ex- 

 tremely defective ; but what we do know concerning the so-called Filaria piscium, Tri- 

 china spiralis, and other immature Nematodes is confirmatory of this belief. More- 

 over, in his recent work on "Entozoa," Dr. Cobbold, speaking of the Ascaridcs, remarks, 

 " In aU situ.ations Avhero there is an abundant Avater-supply these parasites are more 

 particularly common ; and it is Avell known that the lowlands of Holland and the lake 

 districts of Sweden are eminently favourable to their existence. All this is explicable 

 enough from Avhat we now know respecting the conditions which are essential for the 

 rearing of the larvae ; but, as I have before observed, it is almost certain that the human 

 body becomes infested, not by the drinking of water which may contain the sexually 

 immature embryos, but by feeding upon the flesh of some quadruped, fish, or fowl which 

 happens to represent the so-caUed intermediate host" (p. 313). 



Some additional points in the anatomy of the members of this group, to which I will 

 briefly allude, seem to strengthen the view I have been endeavouring to enforce. In the 

 first place, the integuments have a greater proportional thickness than in the recognized 

 parasitic forms ; and in the next, there is a marked difference in the number of ova or 

 young" produced : whilst the entozoid species are most prolific, furnishing ofi'spriug by 

 hundreds, thousands, or even millions, in these free Nematoids the ova are relatively very 

 large and few in number, being easily countable, and, for the most part, seen in single 



vations concerning the animals found in this last habitat, before we can be certain that they belong to any of the 

 genera of free Nematoids, since it is perfectly certain that in his genus Bhubditis Dujardin includes many and most 

 diverse types. Speaking of these Nematoids and the Earth-worm, he says, " Je I'ai vu plusieurs fois, soit a Paris, soit 

 ii Eennes, se developper en quantitc prodigieuse, et former des amas blanchatres dans des vases on j'avais conservL- des 

 lonibrics avcc do la mousse et de la terre humido." Moreover it appears from the interesting experiments of Davaine 

 ('Recherches sur I'Anguillule du ble nielle',' Paris, 1857, p. 64) upon the young of the Vibrio tritici, that their 

 chitinons integument eflFectually protects them from injury within the alimentary canal of the cojd-blooded animals. 

 This was ascertained by experiments upon the Frog, the Triton, tlie Salamander, and a fish {Cyprimis auratus) be- 

 longing to the same genus as that in which the Borylaimi were found by Dujardin. Davaine says, " Ingerdes dans 

 Testomac de ces animaux, soit sfeches, soit humides et vivantes, les anguillules de la nielle out parcouru tout Ic tube 

 digestif, sans avoir subi d'alteration ; elles ont etc evacuees on retrouvees dans le rectum, privees de mouvcments, 

 mais non de la vie, dont elles u'ont par tarde a reprendre les manifestations, apres avoir e'te place'es dans I'eau pure." 

 This seems to afford a very probable explanation of the accidental presence of these free Nematodes uninjured within 

 the alimentarxj canals of certain of the lower animals, though it does not at all account for their presence within 

 the general cavity of the body of the earth-worm, as reported by Dujardin, or of Na'is albida, as related by Carter. 

 It should be remembered, however, that the general cavity of the body in these animals is not a shut sac, since it 

 communicates with the exterior by raeaus of certain ciliated tubes, called by Dr. Williams (Phil. Trans. 1858, p. 93) 

 "segmental organs.". In these tubes of the earthworm a parasitic Nematoid (Bicelis Jilaria, Duj.), is known to exist 

 in great abundance. The young of this animal might work their way through the patent terminations of the tubes 

 into the abdominal cavity of their host ; and it is even possible that minute free Nematoids might also work their 

 way inwards, through these tubes, into the abdominal cavity of both Kais and Earthworm. 



