(see page 28 ) the edge hooks have a special loop (Bychowsky calls it a 

 buttonhole, nobis) through which the point of the hooks passes. In many 

 Polystomatidae we easily observe these loops, and what is especially 

 significant is that they often diverge ( are displaced, nobis ) from the 

 hooks themselves and lie somewhat to the side of the latter. This phe- 

 nomenon was observed not only by us but also by a number of other re- 

 searchers. Thus, a number of drawings are reproduced in the works of 

 Osaki to show this (Osaki, 1935a, Figs, 20, 25 and 26). Furthermore, 

 Osaki writes that in Polystomoides ( = Neopolystoma ) exhamatunn Osaki, 6 

 "loops" which sloughed off their edge hooks (Fig. 289) lie on the anterior 

 end of the attaching disc between the anterior suckers. Thus instead of 

 the normal 16 edge hooks which were in the larvae the adult individuals 

 retain only 10 (4 lying on the posterior end and 6 in the suckers) having 

 however, all 16 "loops. " We observed the same picture of 2 pairs of 

 "loops" of the edge hooks in a number of Hexabothriidae (Fig. 290). What 

 is most interesting in this case is that one of these pairs was located in 

 the small suckers approximately at the very same places where grown edge 



fl/«w 



Fig. 290. Squalonchocotyle sp. from the gills of Squalus acanthias L,. 

 from the region of the Island of Shikotan (Kurile, shallow waters). 

 A--Schematic drawing of the posterior end [of the "outgrowth" of the 

 attaching disc (location of the "loops or buttonholes" of Bychowsky, nobis ] ; 

 B- -Middle hook and "loops" of the same sample. 



hooks lie in the large ones, i.e., fully corresponding to the suppositions 

 of Cerfontaine! The second pairs of "loops" lies on the posterior edge of the 

 disc near the pair of middle hooks, similar to what is observed in the 

 larvae of Microcotylidae (see page 204 ). Hence, one can make the very 

 probable conclusion that the larvae of Hexabothriidae have 10 pairs of edge 

 hooks and one pair of middle hooks (the latter perhaps is incepted later), i. e. , 

 they differ in chitinous armature from the larvae of Diclybothriidae only 

 by the absence of the second pair of middle hooks. As regards the rennaining 

 characteristics of the larvae, one can suppose that they are similar to the 

 ones of Diclybothrium. The eyes constitute an exception about which we 

 cannot say anything definite. It is more probable that they are either 

 completely absent or have a different form than in Diclybothrium for if it 



488 



