formed on the attaching disc and functionally replacing both the 

 chitinous armature (playing the role during the early stages of the life 

 cycle) and "the attaching properties" of the disc itself. It would have 

 been tempting to visualize the formation of such a type of attachment 

 as a subsequent stage of development of the disc-sucker equipped with 

 separate suction pits which arise as a result of the separation of the 

 disc by septa; however, this is not true. The fact that the suckers of 

 the disc represent new formations is confirmed easily by the fact that 

 the type of their inception at the place of the edge hooks (see page 185 ) 

 does not correspond to the formation of the suction pits on the disc- 

 sucker, which are incepted toward the center from the edge hooks. 

 Thus, it is a special line of evolution connected, as a matter of fact, 

 as is known to us, with the change to parasitizing the new group of 

 hosts, Amphibia and Reptilia, However, the sanne type of new formation 

 is also characteristic for one very old group of monogenetic trematodes, 

 Hexabothriidae» pertaining to another trunk of development of Monogenoidea. 



One more branch of the first line where Acanthocotylidae 

 belong is characterized by a special type of development of the attaching 

 apparatus. About it one should only say now that here the primary disc 

 with the typical chitinous armature is functionally replaced by an 

 attaching disc which is formed completely anew. As a matter of fact, 

 more in detail will be said later about this line of evolution (see pages 

 383 and 456). 



In conclusion, within the limits of the first trunk of mono- 

 genetic trematodes we see four basic directions of which the first three 

 comprise a huge (in relation to the over-all) nunnber of very diversified 

 species. Let us not forget that for the time being we are speaking only 

 about the ways of evolution of the attaching apparatus, but whether or 

 not they correspond basically to the ways of evolution of the monogenetic 

 trematodes as a whole must be subjected to further discussion. 



Within the limits of the monogenetic trematodes which are 

 characterized by the larva of the second type (see page 100 ), the basic 

 lines of development are considerably more homogeneous. One can p. 331 



consider that the larval hooked arnaature, in principle very close to that 

 of the first type, functions during the early stages of development and 

 then for the entire group as a whole its replacement by new formations -- 

 clamps, (see page 161 ) or a connbination of a clamp and a sucker united 

 together with a prevailing action of either a chitinous clamp or a muscular 

 sucker, is characteristic. One cannot fail to note that among almost all 

 species pertaining here the chitinous hooked armature loses its significance 

 earlier and earlier so that the separate forms are even partially deprived 

 of it already in the free -swimming larval stage (see page 201 ). As regards 



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