armatum takeB place in approximately 2 weeks. The larva, which has 

 just emerged from theegg ,is torpedo-shaped and is about 0. 4 mm in 

 length when the width of the body is about 0. 18 mm. The attaching disc 

 is clearly delineated from the rest of the body and has a length of 0. 08 

 mm and a width of about 0. 16 mm. There is a ciliary epithelium dis- 

 tributed in three zones on the surface of the body of the larva. The first 



zone occupies the surface of the 

 anterior end of the body, extends 

 posteriorly to the level of the 

 pharynx and consists of two sections 

 of ciliary epithelium lying along the 

 edges of the cephalic end and ex- 

 tending sonnewhat onto the dorsal 

 and ventral surfaces of the body. 

 Both of these sections begin some- 

 what away from the anterior end so 

 that the extreme anterior end is 

 free of cilia. The second zone be- 

 gins somewhat above the middle, 

 extends posteriorly almost to the 

 beginning of the attaching disc and 

 is located also in two sections 

 along the sides of the body and also 

 extending somewhat onto the dorsal 

 and ventral surfaces. The third zone is located on the attaching disc, and 

 consists of two lateral sections which begin on the anterior edge of the 

 disc and terminate somewhat just short of its posterior end. 



Fig. 220. Diclybothrium arnnatum 

 Leuckart, free-swinnming larva. 

 (According to Bychowsky and 

 Gussew, 1950). 



The anterior end of the body bears 2 pairs of rather well- 

 developed eyes located in front of the pharynx. The posterior pair is 

 somewhat larger than the anterior. The pharynx is more or less 

 rounded, about 0. 04 mm in diameter. From it extends the circular 

 intestine of somewhat elongated shape which reaches posteriorly almost 

 to the anterior edge of the attaching disc. The excretory system was not 

 discovered during the studies of both samples. The attaching disc bears 

 a powerful and complex armature consisting of 7 pairs of chitinous hooks 

 of three different types (Fig. 221--B.B.). Among them five pairs are 

 of the same shape and size and are located along the edge of the disc and 

 two pairs differing (from each other, nobis) in shape and sizes and sharply 

 differing from the edge ones lie in the nniddle section of the disc. The 

 lateral hooks resemble those of the dactylogyrid-type; they have a strongly 

 developed hooked part proper and a rather thin, long handle. The in- 

 terior offshoot of the hooked part is widened in the middle and its 

 sharpened free end is oriented toward the same side as the handle. The 

 sharp points of the lateral hooks are rather strongly curved. Each 

 lateral hook is equipped with a chitinous loop of rather large size 

 customary for all highest monogenetic trematodes. The 1st pair of 



210 



