similarities based on parallelism which arises during the course of the 

 historical process of adaptogenesis. 



Three orders- -Dactylogyridea Bychowsky, Tetraonchidea 

 Bychowsky, and Gyrodactylidea Bychowsky enter into the subclass. 



1. Order DACTYLOGYRIDEA, Bychowsky, 1937 

 Monopistocotylea Odhner, 1912, part . 

 Polyonchoinea^ which have larvae with 12 to 14 edge hooks 



1 



In connection with the removal of Tetraonchidae and families close to them 



from this order, the indication of 16 edge hooks is excluded. 



on the attaching disc and are, for the most part, equipped with 4 eyes. 

 The attaching apparatus among adult forms consists of a chitinous 

 armature located on the attaching disc: the latter, in a number of species, 

 changes to a powerful sucker. The copulatory organ is either with a 

 chitinous pipe or unarmed. The cephalic end is equipped with two 

 groups of cephalic glands often forming special glandular pulvillae 

 "pillows" which serve for attachment; sometimes the latter form 

 sucker-shaped pits (or cavities, nobis). In the last case these "suckers" 

 are never linked or connected with the buccal opening" (Bychowsky, 1937). 



Just as does the diagnosis of the subclass Polyonchoinea, the pre- 

 sent diagnosis demands a number of additions and clarifications. The 

 indication of the presence among the larvae of 12 edge hooks is based 

 on information about Protogyrodactylidae and Calceostomatidae; 

 inasmuch as we doubt the correctness of the data concerning Proto- 

 gyrodactylidae (see page 360) and we are not sure of the correctness of 

 the attribution of Calceostomatidae to this order (see page 363 Kit 

 probably would have been more correct to consider that the larvae of this 

 order have only 14 hooks. One must also explain that the development 

 of Microbothriidae has not been studied and they are attributed to this 

 order as a supplement on the basis of the similarity between their 

 anatomical structure and that of the families, which clearly belong here, 

 (see page 385) conditionally. As regards the attaching formations of 

 the anterior end of the body, it is characteristic that they are always 

 paired, although basically the cephalic glands decrease in number and 

 are gradually replaced by muscular sucker-shaped formations. In 

 separate cases a secondary increase in the number of glands, as well p. 345 



407 



