in the shape ol a simple transversely elongated stick, in the shape of a 

 triangle, in the form of a T or inverted T of more complex fornn. Thus, 



for instance, in the group of D. 

 ' ■ kulwieci Bychowsky the supple- 



mentary plate consists, as it were, 

 of two halves connected by a small 

 membrane and the part which faces 

 the lower edge of the disc has the 



R^^ 



OOlnn 



=^ 



Fig. 143. Diagram of the develop- 

 ment of the middle plate of Dactylo- 

 gyru3 » 



Fig. 144. Dactylogyrus longicopula 

 Bychowsky, attaching armature of a 

 young worm in the process of develop- 

 ment frona the gills of Schizothorax 

 intermedius McCl. fronn the river 

 Varzob (Tadjikistan, SSR). 



shape of an inverted fleur-de-lis, whereas the upper one is bent in the shape 

 of a V or U. As an exception, there exist connecting plates elongated longi- 

 tudinally in the shape of a stick, as for instance among D. simplicimalleata 



^^^^::^=^ -^^^^TT^ 



Fig. 145. The shape of the supplementary plates of the attaching discs of 

 various species of Dactylogyrus. • A— D. si mplicimalleata Bychowsky; 

 B— D. bicomis Malewitzkaja; C— D. cryptomeres Bychowsky; D— D. alatus 

 Linstow; D. facetus Gussew; E— D. pa rabramis Gussew; F— D. zandti 

 Bychowsky; G — D. difformis Bychowsky; H— D. minor; I— D. linstowi 

 Bychowsky; J — D. affinis Bychowsky. 



Bychowsky. In spite of all the different forms of the supplementary plates, 

 one can establish on the basis of the observation of their development that 

 these are homologous formations, ^ the evolutionary development of which 

 takes place in a comipletely determined fashion. The supplementary plate 



p. 145 



154 



