78 MR. H. CHARLTON BASTIAN'S MONOGRAPH 
leading helminthologists of the present day, who are almost all now disposed to belieye 
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 t; 
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 Nem. 
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 Ascarides, remarks, 
“In all situations where there is an abundant water-supply these parasites are more 
particularly common ; and it is well known that the lowlands of Holland and the lake 
districts of Sweden are eminently favourable to their existence. All this is explicable 
enough from what we now know respecting the conditions which are essential for the 
rearing of the larve ; 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-called intermediate host ” (p. 313). 
Some additional points in the anatomy of the members of this group, to which I wil 
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 ovaor 
young! produced: whilst the entozoid species are most prolific, furnishing offspring by 
hundreds, thousands, or even millions, in these free N ematoids 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 genu 
(‘Recherches sur l'Anguillule du blé niellé Pari 
the Triton, the Salamander, and a fish (Cyprinus auratus) w 
rylaimi were found by Dujardin. Davaine says, “ Ingérées dant 
soit humides et vivantes, les anguillules de la nielle ont parcouru tout le tube 
h-worm, as reported by Dujardin, or of Maïs albida, as related by Carter 
| or by means of certain ciliated tubes, call " il. Trans. 1858, p.99) 
“segmental o; o» ; , called by Dr. Williams (Phil. rans. ig 
Meam "gans.” In these tubes af the earthworm à parasitic Nematoid (Dicelis filaria, Duj.), is known to - 
into the abdom; ... Joung of this animal might work their way through the patent terminations of the tub? 
abdominal cavity of their ; and it i : \ : work their 
way inwards, through these tubes ics. a 7 even possible that minute free Nematoids might also 
pc "Des, into the abdominal cavity of both Nais and Earthworm. | 
the general cavity of the body in these animals is not a shut sac, since — 
