55 



CHAPTER VII. 

 CYCLOPHYLLIDI^:. 



Cyclophyllidice (Tieniidae). Several species are found in 

 man and two of them are common. Man is for one 

 species Echinococcus only the intermediate host. In 

 the other Tceniidce he is the definitive host ; in some, as 

 Tcenia solium, though usually the definitive host, and 

 infected with the sexually mature worm, he may harbour 

 larval forms cysticerci and, therefore, can act also as 

 the intermediate host for that species. 



The Cyclophyllidiae differ from the Dibothriocepha- 

 loidea in the course of development as well as in the 

 structure of the scolex and proglottides. 



The eggs are either passed from ripe proglottides whilst 

 still in the intestinal canal of their host, or are deposited 

 by the proglottis on the ground, or in water, after the 

 ripe segment has escaped from the intestine. 



These eggs at the time they are passed have lost their 

 outer part, so that only the embryo in its embryonic 

 capsule oncosphere is to be seen. 



It is a part only of the egg, and not, as is commonly 

 supposed, the tapeworm egg. Remnants of the remainder 

 of the egg sometimes may be seen still attached to the 

 capsule of the oncosphere. 



The embryo at the stage which it has reached when 

 the oncosphere is passed has a definite head and is 

 armed with three pairs of nearly straight hooklets. 



The embryonic capsule is thick and in many cases 

 striated radially. The cells covering the oncosphere, if 

 any remain after the "egg" is passed, soon disappear and 

 the embryo remains quiescent in its capsule. 



