The second group, that is supplementary (or compensating 

 discs),, is represented by the following disc-shaped growths or organs 

 which lie one by one on the ventral surface of the disc. They are located 

 on the attaching discs in front of the middle hooks and the apparatus which 

 joins them. Each one of these growths is equipped with special muscula- 

 ture which allows it to change its size and degree of convexity and is also 

 equipped with chitinous concentric rings (Lamellodiscus , Fig. 34) or con- 

 centric rows of individual chitinous straight spines (Diplectanuna, Fig. 14) 

 which serve for the process of attachment along with the system of lateral 

 and middle hooks. 



30 





Fig. 34. Lamellodiscus elegans Bychowsky, 

 adult worm from the gills of Sargus annularis 

 (L. ) from the region of Karadaga (Black Sea). 



Fig. 35. Sphyranura osleri 

 Wright, adult worm from 

 the skin of Necturus sp. 

 from the Huron River, 

 (Michigan, U.S.A.). 



The secondary disc of Acanthocotyle (Fig. 18, A) which replaces 

 the primary attaching organs functionally (see pp. 36 and383 ) has a structure 

 similar to the secondary discs of Diplectanum. 



23 



