quarters of the length of the body a pigmented eye is located lying mesially 

 from the ventral side of the body. This eye has the shape of a slightly 

 elongated rectangle and apparently is fused from two; the sizes are about 

 0. 001 X 0. 005 mm. The eye, well-developed in the larva, disappears 

 rather quickly after the attachment of the latter. The digestive system is 

 represented by a strongly developed pharynx and a sac -like intestine. 

 The pharynx is rounded and is about 0. 03 mm in diameter. The intestine, 

 which occupies approximately the third quarter of the length of the body, 

 has a narrowing in the middle part and a small invagination in the middle 

 of the posterior edge forming, in this fashion, 2 posterior lobes. During 

 further development these lobes give rise to two intestinal branches. The 

 attaching disc of the larva is equipped with a pair of larger (middle) hooks 

 and 5 pairs of edge hooks (Fig. 223). The large hooks are rather 

 massive with a hard, straight handle and rather powerful point. Their 



sizes are about 0. 028 to about 

 0. 03 mm. The edge hooks have 

 a tender, flexible handle and 

 their terminal little hook is of 

 a different form than among all 

 the preceding species: it is 

 more elongated with a straight 

 edge. The sizes of edge hooks 

 are about 0. 2 mnn. During 

 further development the chitinous 

 hooks of the larva suffer different 

 fates. The large hooks which lie 

 at the very posterior end of the 

 disc and one pair of edge hooks 

 which is located side by side 

 with them are preserved during 

 the entire life of the animal 

 without any change in shape and 

 sizes. The fate of the second to 

 fifth pairs of edge hooks is 

 completely different. Very soon after the attachment of the larva, the 1st 

 pair of attaching clamps begins to form on the place and foundation of the 

 2nd pair of edge hooks and then subsequently in the place of the 3rd pair 

 of hooks --the 2nd pair of clamps, etc. until all 4 pairs of clamps charac- 

 teristic for the adult forms are finally formed. Simultaneously with the 

 beginning of the formation of the 1st pair of clamps on the attaching disc 

 a pair of large middle hooks which have a final form similar to the one in 

 Dactylogyrus, with very powerful exterior and somewhat weaker interior 

 offshoots, is incepted and begins to form. Thus the adult form retains 2 

 pairs of hooks of the larva without any changes and acquires one pair dur- 

 ing the postembryonic development. The tempo of development of 

 attaching clannps was not followed through by us; however, we must note 

 their characteristic peculiarity, i, e. , their ability to grow. One can 



Fig. 223. Mazocraes alosae Hermann, 

 attaching armature of the free- 

 swimming larva. 



p. 196 



213 



