118 INVERTEBRATE ZOOLOGY 



are duplicated successively in an undivided body. A secondary 

 strobilization is known to take place in some cestodes wherein 

 the original proglottids undergo a secondary subdivision, each 

 giving rise to a number of proglottids which may eventually 

 separate as independent strobila. One proglottid in each new 

 chain becomes modified as a pseudoscolex. 



Subclass Cestodaria 



The Cestodaria or monozoic cestodes rather closely resemble 

 trematodes, but the lack of digestive organs necessitates their 

 inclusion as a subclass along with the true cestodes. There is no 

 sharp differentiation between scolex and proglottids in the Ces- 

 todaria, and but one set of reproductive organs usually occurs 

 in each individual. They occur in both marine and fresh-water 

 hosts. Members of the genus Archigetes become mature in 

 oligochaetes, Gyrocotyle in the spiral valve of elasmobranchs, 

 and Caryophyllaeus, Glaridacris, and Amphilina in the body 

 cavity or digestive tract of fishes. The organ of attachment is 

 variously modified. 



Subclass Cestoda (s. sir.)^ 



The poly zoic cestodes include all the typical tapeworms which 

 have a scolex followed by a succession of organs usually divided 

 in chain fashion into a series of proglottids. These cestodes 

 reach the adult state in the digestive tract of vertebrates, every 

 class from fishes to mammals serving in the capacity of host. 

 There is no restriction to a single type of larval host as in the 

 digenetic flukes, for a wide variety of both invertebrates and 

 vertebrates act as host for larval tapeworms. 



Reproductive Organs. — Each proglottid is furnished with a 

 complete set of reproductive organs (Fig. 66 B), and in some 

 instances two sets occur in each. The male organs consist of 

 from one to more than a hundred testes (Fig. 67) embedded 

 within the parenchyma and connected by vasa efferentia and vas 

 deferens with the cirrus which communicates with the outside. 

 The genital ducts of both sexes usually open in a common genital 

 pore which is either on the lateral margin of the proglottid or 



^ Sensu stricto indicates that a word is used in a limited or restricted 

 sense. In this instance the word Cestoda is used for the entire class, but 

 in a restricted sense the same word is used to designate the true cestodes 

 from the Cestodaria. 



