ii 4 



SYSTEMATIC ZOOLOGY 



proglottides; it contains ganglionic masses, often well developed, 

 corresponding to the brain, which occur in none of the segments. 



Furthermore, it is clear that 

 in these tapeworms the 

 whole worm corresponds to 

 the simpler Cestoda, which 

 consist of a single piece, 

 for there are intermediate 

 types, where the organs 

 are repeated, but where no 

 external proglottides are 

 formed. These facts would 

 suggest that the tapeworm 

 is a single individual. The 

 tendency to-day, however, 

 is to regard the common 

 tapeworm as a colony like 

 the strobila of the Scypho- 

 medusa, — the scolex thus 

 corresponding to the scy- 

 phistoma, and the proglot- 

 tides to the young medusas 



J o 



or ephyrae, i.e. they become 

 the sexually mature indi- 

 viduals. 



The development of the 

 Cestoda takes place in al- 

 most all cases bv means of 

 two hosts, one in which it 

 always remains an embryo 

 or larva, and the other in 

 which it becomes an adult. 



Fig. 104. Tcenia solium, the pork tapeworm, cap. The eggs develop into etn- 

 scolex or head. (After Leuckart, from t'arker and forves provided with hooks 

 Haswell's Manual.) , , 



and on being taken into the 

 alimentary canal of the proper host, they bore through the 

 lining of the intestine and presumably enter the blood vessels, 

 through which they are carried to the various organs of the 

 body, such as the muscles, the brain, the liver ; there a cavity 



