the clamps and the clamp-suckers formed anew, they are located not 

 only on the primary attaching disc but also on the sections of the body of 

 the animal lying above it, which are often not even separated from its 

 basic part. 



Thus>the second trunk of the development of monogenetic 

 trematodes is much more homogeneous in the sense of a general 

 direction of the evolutionary development of the attaching apparatus, 



However, examining the nature and the direction of evolution- 

 ary changes within the limits of the given type of attaching armature 

 we can note a number of important tendencies of both qualitative and 

 quantitative nature. 



The qualitative changes observed in the given type of develop- 

 ment are reduced to the gradual complication of the initially simply- 

 formed clamp (see page 32), both by way of the increase in the number 

 of separate chitinous parts with the preservation of the basic plan of 

 the typical clamp, and by v/ay of the growing together of the separate 



parts and of forming a complex capsule for the movably -joined halves. 

 At the same time, we also observe the separation of the clamp proper 

 from the sucker, and this process proceeds in the direction of the 

 complete disappearance of the clamp of the sucker which is separated 

 inside in the beginning. Finally, one often observed the differentiation 



in the sizes of the clamps and one large pair assumes the basic function 

 of the attachment of the animal (Bychowsky and Nagibina, 1954). The 

 qualitative alterations proceed in the direction of an increase in the 

 number of attaching clamps, but the reverse process apparently also 

 plays a role in separate cases (page 442 ). Among specieswith a con- 

 siderable number of clamps, attention is drawn to the fact that the 

 latter are different in origin in spite of their complete morphological 

 similarity. Thus, the first four pairs of the clamps are formed on the 

 base of the initial or primary hooked apparatus, whereas the subsequent 

 ones represent new formations (see Dogiel, 1954a and also page 161 ). 

 Also important is the tendency toward disruption of the asymmetry of the 

 attaching formations by way of the unequal number of the inceptions of the 

 attaching clamps on each aide of the body at the time of their individual 

 development. This phenomenon practically leads to a different 

 asymmetry of the animals and this process can proceed differently (see 

 page 442). No such type of evolution is observed within the limits of the 

 first trunk of monogenetic trematodes. This peculiarity, encountered 

 in the second type, underlines the circumstance that here generally 

 takes place the process of autonomization of separate parts of the 

 attaching apparatus in contrast to greater and greater integration noted 

 within the limits of the first type. 



388 



