and extending into both of its valves and representing a spring, so to speak, 

 now bending, now straightening. In each half of the clamp along the sides 

 of the valves lies one curved band as if supporting the edge. These four 

 bands lie in such a way that at the place of junction of both halves of the 



clamp they articulate in pairs 

 from each side so that the 

 corresponding bands of both 

 clamp halves or valves ar- 

 ticulate with each other. Their 

 free ends extend along the 

 edge of the valve and reach 

 under the ends of the middle 

 band. At the place of ar- 

 ticulation of each two lateral 

 bands lies one (usually short) 

 band which unites with them 

 and with its free end extending 

 toward the middle band along 

 the outer surface of the dorsal 

 clamp of the valve. For the 

 most part, the middle band p. 33 



is linked to the others by special growth or organs in the places of their 

 articulation. From those which have such structure of attaching clamps 

 result, on the one hand, the types which distinguish themselves by the 

 complication of form as well as by the increase in the number of chitinous 

 parts, and on the other hand simplified attaching valves in which chitinous 

 details disappear. As a rule the attaching valves are located symmetrically 



_ 



The details about this appear in the chapter "Taxonomic System of Mono- 

 genetic Trematodes',' (pages 416 to 447 ). 



Fig. 38. Diagram of the structure of the 

 primitive attaching clamp. On the left 

 the clamp is fully open, on the right- -it 

 is partially closed. The chitinous parts 

 are in black, the musculature is cross- 

 hatched. 



on the disc (for instance Microcotyle, 

 Fig. 23), however, in a number of 

 cases there are fewer on one side of 

 the disc (for instance Heteraxine, 

 Fig. 40) or they are totally absent 

 (for instance Gastrocotyle, Fig. 7), 

 which, in this connection, leads to 

 the formation of asymmetrical attaching 

 discs. The formation of asymmetrical 

 discs armed with valves can originate 

 in two ways. In the first, apparently 

 the more widespread asymmetry re- 

 sults by the way of formation of an in- 

 creasingly smaller nuniber of valves on the one side of the disc up to ces- 

 sation of their inception altogether during the time of development. With 



Fig. 39. Typical attaching 

 clamp. Explanation in text. 



26 



