PLATYELMINTIIEX. 175 



becomes (Bothriocephaltcs proboscideus) a cuticular layer. Between 

 the six-hooked embryo and the outer layer of cells one or more 

 thick membranes become deposited (E. van Beneden). The eggs are 

 carried out of the alimentary canal in the proglottis and transported 

 to various situations on land or in water. They usually remain 

 within the proglottis, invested by their thick shell, till taken up 

 into the alimentary canal of a suitable host, or they may be swallowed 

 after the death and decay of the proglottis. They are subsequently 

 hatched after their shell has become softened by the action of the 

 digestive fluids. 



Before proceeding to describe their further history, the close 

 resemblance between the first developmental stages of Cestoda, 

 especially in the case of the ciliated larvae, and those of Trematoda, 

 may be pointed out. 



In both there is a ciliated larva, and in both there is developed 

 within the ciliated skin a second larva, which becomes freed by the 

 stripping off of the ciliated skin. 



The type of development has moreover many analogies with that 

 of the Nemertine larva of Desor, p. 163 (cf. Metschnikoff), and is pro- 

 bably like that an abbreviated record of a long history. 



The suitable host for the six-hooked embryo to enter is rarely tlie 



FIG. 96. DIAGRAMS OF VARIOUS STAGES IN THE DEVELOPMENT OF THE CESTODA. 

 (From Huxley.) 



A. Cysticercus. B. arid C. Cysticerci in the everted (B) and inverted (C) condition. 

 D. Coenurus. E. and F. Diagrams of Eckinococcus. It is most probable that Taenia 

 heads are not developed directly from the wall of the cyst as represented in the 

 diagram. G. Six-hooked embryo. 



same as the host for the sexual form. The embryos having become 

 transported into the alimentary canal of such a host, and become 

 free, if previously invested by the egg-shell, soon make their way, 

 apparently by the help of their hooks, through the wall of the 

 alimentary tract, and are transported in the blood or otherwise into 

 some suitable place for them to undergo their next transformation. 

 This place may be the liver, lungs, muscles, connective tissue, or 

 even the brain (e.g. Coenurus cerebralis in the brain of sheep). 



Here they become enclosed in a granular deposit from the 

 surrounding tissues, which becomes in its turn enclosed in a connec- 

 tive-tissue coat. Within lies the solid embryo, the hooks of which 



