stages of development (on the 3.verage apparently before the appearance 

 of the second half of the base section). This plate is incepted in the shape 

 of a thread curved transversly and grows in length as well as in width. 

 Among different species its development is somewhat different: in some 

 it simply reaches its final shape and size gradually, as for instance 

 among D. anchoratus (Dujardin) and among others it first curves in the 

 middle depending upon its final shape, for instance D. longicopula Bychowsky 

 (Fig. 144). ~ 



X.^^^ 



Fig. 142. Dactylogyrus anchoratus (Dujardin), development of middle 

 hooks of the disc. Enlarged 375 times. (According to Kulwiec, 1927). 



This terminates the development of the attaching apparatus among 

 the group of Dactylogyrus which lacks a supplementary plate. 



- . . 



In the development of worms of this group, Kulwiec (Kulwiec, 1927) 

 distinguishes three stages (four, to be exact, because she subdivided her 

 second stage into tw^o periods). As her research correctly indicates, 

 these stages are artificial but very convenient in the determination of 

 development and comparison of the tempo of aevelopment among different 

 species. The signs which differentiate the stages are: first stage--the 

 larva (which has lost its ciliary epithelium and begun to grow) until the 

 appearance of the inceptions of the middle hooks; the first part of the 

 second stage is characterized by the appearance of the middle hooks and 

 extends until the inception of the connecting plate; the second period of 

 this stage begins from this nnoment and terminates at the beginning of 

 the third stage which starts from the appearance of the interior excrescences 

 of middle hooks. 



The supplementary plate, which exists in the second group of 

 Dactylogyrus appears as the most variable part of the attaching armature 

 in shape as well as in size (in relation to the rest of the arnnature) (Fig. 

 145). Among adult Dactylogyrus one can observe the supplementary plate 



153 



