differently than in Dactylogyridae and resembles, in its action, the one of 

 the nriore highly organized groups --Calceostomatidae, Monocotylidae, 

 Capsalidae and others. At the same time, because of the presence of a p. 396 



ring of plates the disc begins to differentiate itself into two parts--the 

 peripheral fringe and the "sucker" proper which is characteristic for 

 Monocotylidae and which never occurs in Dactylogyridae. The plates of the 

 disc themselves are neoplasms {new growths, nobis) which do not have any 

 analogies in any other group of Monogenoidea. Inasmuch as these formations 

 are of important adaptive significance, they should not be evaluated as a 

 character of the second order. As regards the remaining chitinous arnnature, 

 the presence of the connecting plate between the middle hooks, which un- 

 doubtedly resemble the one in Dactylogyridae, Tetraonchidae, and other 

 close families --probably points to the homology of these formations. How- 

 ever, we do not have sufficient bases to consider it as a deciding significance, 

 because the absence of this character in Tetraonchoididae, Monocotylidae 

 and other families of the corresponding group is either a secondary 

 phenomenon, i.e., a result of reduction, or, what is more likely, the 



consequence that the necessity for the 

 strengthening of the system of the 

 hooks during the development of the 

 corresponding forms did not arise be- 

 cause of the short term of their 

 functioning during the period of the 

 individual life of the worms. The 

 functional significance of the supple- 

 mentary plate connected with the ring 

 of the plates and located at the place 

 of its interruption is not fully under- 

 standable. It is possible to think that 

 it plays a certain role in the mechanical 

 fixation of the upper edge of the disc, 

 and also serves for the attachment of 

 the musculature which extends into the 

 disc fronn the body of the animal. 

 Thus, this plate probably fulfills the 

 same functions as the corresponding 

 one in Tetraonchoididae. To say that 

 it is homologous to the one of the 



0.1 MM 



Fig. 287. Bothitrema bothi 



(MacCallum), general view of the 

 attaching disc of an adult worm from latter would be very tempting, but 

 the gills of Lophopsetta maculata without the materials on the develop- 



(Mitch.) from the region of Woods ment of both groups this cannot be con- 



Hole (Atlantic Ocean). firmed. At any rate its presence 



forces us to consider more attentively. 

 the probable closeness of Bothitrema to Tetraonchoididae (see page 394 ). 



474 



