252 



PLATYHELMINTHES. 



in consequence of dirty habits. * As soon as the egg membranes are 

 digested or burst by the action of the juices of the stomach of the 

 new host, the embryos, or onchospheres as they are called, which 

 have been thus set free, bore their way into the gastric or intestinal 

 vessels by means of their six (rarely four) hooks, the points of which 

 can be approached and removed from one another over the periphery 

 of the small globular embryonic body (Fig. 205, I). When they are 

 once within the vascular system, they are no doubt carried along 

 passively by the current of blood, g,nd transported by a longer or 

 shorter route into the capillaries of the different organs, as the liver, 

 lungs, muscles, brain, etc. After losing their hooks, they usually 

 become enveloped by a cyst of the connective tissue of their host, 



d 



Fi'> 205. Stages in the development of Taenia solium to the Cysticercus stage (partly after R. 

 Leuckart). a, egg with embryo ; 6, free embryo ; c, rudiment of the head as a hollow papilla 

 on the wall of the vesicle ; d, bladder- worm with retracted head ; e, the same with protruded 

 head, magnified about four times. 



and grow into large vesicles with liquid contents and a contractile 

 wall. The vesicle gradually becomes a cystic or bladder worm by 

 the formation of one (Cysticercus^ Fig. 205, e) or several (Coenurus) 

 hollow buds, which are developed from the walls and project into the 

 interior of the vesicle (Fig. 205, c). The armature of the tape-worm 

 head (suckers and double circle of hooks) is formed on the inside 

 and at the bottom of this invagination of the wall of the vesicle 

 (Fig. 205, d). When these hollow buds are evaginated so as to form 

 external appendages of the vesicle, they present the form and 

 armature of the Cestode head, as well as a more or less developed 



* The habit of allowing dogs to lick the face and to feed off plates which 

 their owners use is, to say the least of it, an unclean one, and should be 

 avoided. 



t Exceptionally two or more heads are found in some Cysticercus forms. 



