THE CYSTIC ENTOZOA. 51 



the accumulation of serous fluid. It may even happen that both 

 these forms of degeneration attack the same embryo. For the 

 better comprehension of these occurrences of excessive growth 

 and of degeneration in the course of the development of the 

 cestoid embryo, I will distinguish the part of the body of the 

 embryo which becomes distended by the formation of the scolex, 

 by the name of the receptaculum scolicis. Strictly speaking, this 

 receptacle is no other than the embryo itself (see page 37, fig. 19**). 



Whilst the scolex is becoming developed within the receptacle 

 of a cestoid embryo, many and various changes of form may 

 be going on in the embryo itself, pari passu with the vesicular 

 change, and these have given occasion to the erection of the 

 various genera of cystic Enlozoa. 



Those Tsenioid embryos whose receptacle has become dis- 

 tended to sometimes a larger, sometimes a smaller vesicle, have 

 been hitherto included in the cystic genus Cysticercus. If such 

 a Tceniu scolex extrudes itself from its vesicular receptacle, it is 

 obvious that the posterior part of the scolex passes immediately 

 into the vesicle, and the presence of such a caudal vesicle in the 

 scolex of a T&nia has been raised into the generic character of 

 the Cysticerci (figs. 24,25). Exposed to certain external in- 

 fluences, the receptacle of a Tcenia 



scolex becomes distended into a very Fig. 24. Fig. 25. 



large and spacious vesicle, from the 

 inner surface of which, a number of 

 Tcenia scolices develop by budding; 

 this form of cystic worm has been 

 elevated into a genus, Ccenurus. An- 

 other kind of Tsenioid embryo becomes 

 metamorphosed into a vesicle of larger 



or smaller dimensions, from whose inner surface countless scolices 

 pullulate ; these, however, become detached, and lie freely within 

 the cavity of the closed parental vesicle. Upon this form the 

 genus Echinococcus has been founded. 



Fig. 24. Cysticercus cellulosce from the human brain, of its natural size, and with 

 a retracted anterior extremity. Fig. 25. The same Cysticercus extruded, a. The caudal 

 vesicle of the Cysticercus, which is nothing hut the receptactdum scolicis (or hinder end 

 of a Tzenioid embryo), distended into a vesicle by the accumulation of water, b. The 

 retracted anterior end of the body of the Cysticercus contains the taenioid scolex deve- 

 loped by budding within the embryo, c. Thy transversely wrinkled anterior extremity 

 of the Cysticercus. d. Its head and neck, which conjointly form the Taenioid scolex. 



