CESTODA MEROZOA 



227 



The Structure of the scolex is of importance for it forms the basis 

 of the classification of the Cestoda Merozoa. In the tapeworms 

 occurring in the gut of fishes the scolex may have two or four suckers 

 and the neck may be sharply separated from the region where bud- 

 ding occurs. In these tapeworms the scolex is often armoured with 

 chitinous projections and hooks, and the number of the proglottides 

 is usually small. The tapeworms occurring in the mammals {Cyclo- 

 phy Hided) are, with one exception, characterized by a head which 

 bears four suckers at the sides, and, on a projection at the top, called 

 the rostellum, is a crown of hooks. 



ln,exc.ca, tr.excca 



vasde 



Fig. 164. Diagram of a ripe proglottis of Taenia solium, x about 10. From 

 Cholodkowsky. In.exc.ca. longitudinal excretory canal; tr.exc.ca. transverse 

 excretory canal ; vas de. vas deferens ; vag. vagina ; ov. ovary ; y.gl. yolk gland ; 

 sh.gl. shell gland ; ut, uterus ; t. testes ; ln,n. longitudinal nerve. 



As a general rule the more primitive cestodes are found in the 

 lower vertebrates, while the advanced types are found in the mam- 

 mals. The evolutionary stage of the parasite is therefore closely 

 related to that of its host. A notable exception to this rule is Diboth- 

 riocephalus latus, the Broad Tapeworm of man, which belongs to 

 a group of tapeworms occurring more commonly in the guts of 

 fishes. The scolex of Dibothriocephalus has two suckers on either side 

 of the head. These suckers are of the nature of flabby folds sharply 

 distinct from the well-defined cuplike suckers of the Cyclophyllidea. 



The generative organs are of the same type as is found generally 

 throughout the Platyhelminthes. There is a single opening for both 

 male and female organs. From the ootype there leads out a duct which 



