168 



METAZOAN PHYLA 



that though parasitism in the case of the tapeworm has resulted in the 



Nerye 



£xcretory 



Testes 



Progr/oit/'c^ 



Fig. 78. — The beef tapeworm, Taenia saginata (Goeze). A, the whole tapeworm, 

 with many portions omitted, to illustrate the change in the form of segments in different 

 parts of the body. {From Leuckart, "Parasiten des Menschen.") X ^2. ^' scolex and 

 neck in an extended condition. The rostellum bears no hooks and the tapeworm is spoken 

 of as unarmed. {From Leuckart.) X 5. C, proglottid, showing the sex organs. {Also 

 from Leuckart.) X 7. D, ripe proglottid, showing the uterus distended with eggs. 



X 13^. 



disappearance of the 



Posfe//u/rf 

 ■Hooks 

 -Sucker 



Fig. 79. — Scolex of the 

 pork tapeworm, Taenia 

 solium, Linnaeus. {From 

 Leuckart, "Parasiten des 

 Menschen.") X 30. 

 Shows a rostellum with 

 hooks, this being an armed 

 tapeworm. The illustra- 

 tion is not artistically cor- 

 rect, in that the suckers on 

 the two sides are not 

 shown in true perspective. 

 They should be shown in 

 exact side view. 



duction of proglottids 



digestive system and the absence of the processes 

 of ingestion, digestion, and egestion, all of the 

 other processes in metabolism still remain. 

 Absorption occurs over the surface of the body; 

 circulation is from cell to cell; assimilation and 

 dissimilation, secretion, excretion, and elimination 

 are still carried on in the same manner as in the 

 nonparasitic forms. Anal openings have been 

 described in some trematodes and openings from 

 the branches of the gastrovascular cavity to the 

 outside in turbellarians, but the extent to which 

 these can function in egestion is not known. 



196. Reproduction. — Reproduction in this 

 phylum occurs both sexually and asexually. 

 Sexual reproduction is, however, the more usual 

 type. Asexual reproduction in a planarian is 

 usually by transverse fission, but a type of 

 fragmentation has also been described in which 

 the body breaks up into a number of fragments 

 each of which by a process analogous to regenera- 

 tion becomes a complete individual. The pro- 

 is also asexual reproduction. 



