338 THE DEVELOPMENT OF CESTODES. 



These isolated eggs, then, may also find their way into the intestine 

 of their host along with food and drink, and develop further if they 

 have retained their germinal potency, and if the environment be 

 favourable. 



A spontaneous liberation of the embryo does not occur in the 

 Toenice. There are, however, Cestodes, as we have mentioned, in 

 which this does occur, but these all belong to the species with uterine 

 opening, and with large yolk-containing eggs — that is, to the group 

 of the Bothriadse.^ In such cases the embryos (Fig. 177) possess a 

 ciliated coat, by means of which they swim about after Hberation. 

 The process of getting free is easy enough since the eggs of these 

 species are provided at one pole with a little lid (Fig. 171), which is 

 lifted up in obedience to pressure from within. In the Tseniadse 

 there is no such apparatus ; the eggs have a completely closed shell 

 (Figs. 173 and 175), and the embryos only become free after the eggs 

 have been transported into the stomach of an animal where the shell 

 is dissolved or softened by the digestive juices. 



According to my researches on rabbits fed with eggs and proglot- 

 tides of the Taenia serrata of the dog, this liberation takes place in 

 about four or five hours after the transference, and therefore at a 

 time when the fleshy mass of the proglottides has yielded to the 

 digestive juices. When the resistance is less, the time required will 

 also be less. In the species named, which is probably representative 

 of the other cystic tape- worms, it is not strictly a solution of the shell 

 that liberates the embryo, but rather a rupture, which results from its 

 increasing brittleness and the internal movements of the hooks. 



After becoming free, the embryos seem to pass some little time in 

 the stomach. Some at once begin by means of their hooks to bore 

 through the gastric walls to some other organ ; others pass directly to 

 the intestine, whence they also bore their way, usually at some distance 

 from the pylorus. It has not indeed been as yet possible to capture 

 the six-hooked embryo in its passage through the intestinal wall, but 

 this is hardly to be expected in the higher and larger animals ; nor 

 have other animals been as yet investigated in reference to this point. 

 Yet there can be no doubt as to the fact that the embryos do really 

 perforate the wall of the intestine ; ^ they are in their subsequent 



^ The discovery of these ciliated embryos is due to Schubart, who was first able to 

 develop the eggs of Bothriocephalus latus. The early death of this promising young in- 

 vestigator hindered the publication of his observations, so that they were first made 

 known at the Bonn Naturalists' Meeting in 1857, through his friend Terloren, who 

 exhibited Schubart's illustrations. The report of Plainer, according to which a ciliated 

 coating is also to be observed in the early stage of the embryo of Tcenia solium, is based 

 on error (MilUer's Archiv f. Anat. u. Physiol., p. 278, 1859). 



" [Raum (Beitrage zur EntwiokelungSKesph. d. Cvsticeroen," p. 28 : Dorpat, 1883) 



Digitized by wficrosofm 



