360 



THE DEVELOPMENT OF CESTODES. 



FIG. 207. A piece of rabbit's liver with 

 passages of Cysticercus pisiformis. ( x 10.) 



The worms then remain for a while free in the body-cavity, but after 

 some weeks one finds them once more in a cyst hanging usually to 

 the omentum or the connective-tissue covering of the intestines. The 



Cysticerciis tenuicollis of our rumi- 

 nants behaves in an exactly 

 similar way, as we shall after- 

 wards notice in greater detail. 



According to the observa- 

 tions on which we rely, the de- 

 velopment of the cystic worms 

 always begins with the formation 

 of the subsequent bladder. As 

 to the origin of the latter, we 

 have no direct results, but we 

 can hardly be mistaken in regarding it as the enlarged and 

 modified embryonic body. 1 This supposition becomes a certainty 

 when we examine the more microscopic so-called " Cysticercoids," 

 which resemble the above-described bladder-worms in all essentials, 

 and differ only in their minuteness and in the absence of fluid. 



These parasites are found ex- 

 clusively in cold-blooded animals, 

 especially among invertebrates, 

 such as insects and molluscs. As 

 yet but few forms are known not 

 more than a dozen although we 

 have reason to believe that they 

 far exceed the bladder -worms 

 proper in the number of their 

 species. 



In one of these forms, to 

 which we have already (p. 331) 

 referred the Cysticerciis tene- 

 brionis, which is probably the 



Fw. 208. Development of Cysticercus m . ..{.*. 



tenebrwnis (after Stein). A, Embryo after young stage of a Tcema inhabiting 



the hooks are cast off ; , Adult Cysticercus. the mouse Stein has described 



(x about 100.) , , . A , 



the gradual passage of the em- 

 bryonic body into the subsequent bladder. The six-hooked embryo 



1 I believe that I once found the six embryonic booklets near the anterior end of the 

 body of a young Cysticercus pisiformis (" Blasenbandwurmer," p. 120). Professor Ed. van 

 Beneden has, he tells me, been more fortunate, having repeatedly demonstrated these hooks 

 on bladder-worms of Ttenia saginata 0'4 to 0'5 mm. in size. Three times all the six hooks 

 were present in varying position, while in other cases we could see only a few, or only one. 

 [Raum also (loc. cit. supra) appears to have several times found the embryonic hooks in 

 young specimens of Cysticercus pisiformis, whose heads were still undeveloped. R. L.] 



