ANIMAL PARASITES. 47 



of a direct exclusion of the brood in the small intestine as possible, 

 and not as, a priori, improbable. 



As to how long the eggs can be preserved free externally, with- 

 out their embryos losing the faculty of life, we do not yet possess 

 any certain evidence. It appears to me that there is a certain 

 limit, and that not a very wide one ; at least I am convinced by 

 my own experiments, which are confirmed by a statement of 

 Leuckart's, that when the eggs of Tcenia Ccenurus and T. serrata 

 are preserved in water, the vitalizability of the brood is extin- 

 guished in two months. I do not know whether a constant 

 renewal of white of egg may preserve their vitalizability for a 

 longer period, but such a preservation in white of egg is of but 

 little value in practice, or even in itself. It is, consequently, at 

 present an hypothesis quite destitute of proof, to think, as I did 

 formerly, that the eggs might lie through the winter in ice and 

 snow, be carried about in the waters for months by the stormy 

 weather of spring, and yet, at the expiration of this period, 

 develop their brood as soon as they arrive at a suitable intestine. 

 A moderate humidity is certainly favorable to the brood. Desic- 

 cation kills the embryos pretty quickly. After 14 — 24 days 

 Haubner and I did not succeed in producing the evolution of the 

 brood of Tcenia Ccenurus, and Leuckart is even of opinion that 

 complete dryness for twenty-four hours is probably sufficient to 

 destroy the vitalizability of the brood. 



With regard to the fate of the brood of tape- worms, therefore, 

 we now know — that the six-hooked brood contained in the 

 sivalloived eggs of Tsenise is set free in the alimentary canal of 

 animals after the rupture of the egg-shells ; that this rupture, and 

 of course the simultaneous exclusion of the brood, takes place prin- 

 cipally in the stomach, and therefore the egg of the tape-worm has 

 usually once passed the stomach of the animal in question, either 

 from the pyloric or cardiac orifice. 



A question still open is, ivhether this rupture and exclusion 

 is possible before reaching the stomach by the assistance of the 

 masticatory organs, or whether it may occur even in the interior of 

 the small intestine in which the brood was produced ? even when it 

 had never reached the stomach. There is a possibility, but no 

 certainty of the two latter. That segments disseminate their 

 eggs, even in the small intestine, appears from the occurrence of 

 those shrivelled segments of a tape-worm colony, furnished with 

 scars, which are followed posteriorly by still uninjured segments. 



