174 



UNSEGMENTED " WORMS." 



only but many, each of which is capable of becoming an adult tapeworm. 

 'The only known exception to the fact that sexual tapeworms are parasites 



FIG. 56. Life history of Tccnia solium. (After LEUCKART.) 



i. Six-hooked embryo in egg case ; 2. proscolex or bladderworm 

 stage with invaginate head ; 3. bladderworm with evaginated head ; 

 4. enlarged head of adult, showing suckers and hooks ; 5. general 

 view of the tapeworm from small head, and thin neck to the ripe 

 joints ; 6. a ripe joint or proglottis with uterus. 



of Vertebrates, is Archigetez sieboldii^ a simple cestode which is sexual 

 within the small fresh water worm Tubifex rivulorum. 



