which have supplementary plates corresponding to the separate stages of 

 development in D. cornu (Fig. 146): 



The first stage of the development of 

 D. cornu supplementary plate corre- 

 sponds to the plate in 



2nd to plate in 

 3rd to plate in 

 4th to plate in 

 5th to plate in 

 6th to plate in 



(D. cryptomeres Bychowsky 

 (D. pulcher Bychowsky 



(D. varicorhini Bychowsky 

 (D. modestus Bychowsky 



(D. macrocanthus Wegener 

 (D. tuba Linstow 



(D. wunderi Bychowsky 

 (D. nanus Bychowsky 



(D, zandti B ychowsky 

 (D. linstowi Bychowsky 



(D. affinis Bychowsky 

 (D. kulwieci Bychowsky 



The plan of developnnent of the connecting plate in D. cornu 

 obviously does not appear all-embracing. The plates of certain species 

 cannot be included in it; hov/ever, using it as a base we can easily under- 

 stand the process of development of a supplementary plate which has a 

 different shape as for instance among D. crucifer Wegener and D. frisii 

 Bychowsky and_D. minor Wegener and D. chalcalburni Bychowsky. As 

 was already indicated, D. simplicinnalleata Bychowsky, D. bicornis 

 Malewizkaja and_D. facetus Gussew, with an aberrant form of supple- 

 mentary plates the development of which is not clear to us, are exceptions. 



p. 147 



Thus, we have completed the description of the separate 

 parts of the attaching apparatus of Dactylogyrus; certain interrelations in 

 their development still remain to be shown. The middle hooks cind the 

 connecting and supplementary plates develop in relation to each other. 

 One must consider it normal for the majority of the species that in the presence 

 of stronger development of the middle hooks and their extensions, the 

 connecting plate is more developed and the supplementary plate, where it 

 exists at all, is more complex. This normality is a morphological 

 expression of the functional increase in the role of the attaching armature 

 during the attachment of the animal to its host and the mechanical fastening 

 and the establishment of a determined size of the attaching disc. Because 

 of this, the structure of the attaching armiature of different species must 

 be evaluated precisely from this point of view and then the different 



156 



