end of the larva there is a small, rather mobile nose -shaped growth, and 

 approximately at the end of the second third of the body, there are small 

 indentations which delineate the weakly differentiated attaching disc. In 

 D. aculeatum Parona and Perugia the length of the larva (in the straightened 

 condition) is 0. 07 to 0. 10 mm, whereas the width is 0. 03 - 0. 04 mm and among 

 D. similis Bychowsky the length is 0. 06 - 0. 8 mm and the width is 0. 03 - 0. 35 

 mm. The ciliary covering consists of three zones. Its anterior zone is 

 located on the head end and extends posteriorly to the level of the anterior 

 pair of eye spots. It is divided by the nose-shaped growth into two lateral 

 groups of cells and on the ventral side they are closely separated from 

 each other, whereas on the dorsal side they merge at the middle line of 

 the body. The second zone of ciliary epithelium is located along the sides 

 of the body in two parts, which extend posteriorly from the level of the 

 pharynx to the anterior edge of the attaching disc. Both groups of this 

 zone extend to the ventral and dorsal sides of the body but do not touch 



aoiHM 



Fig. 182. Diplectanum silimis Bychowsky, free -swimming larvae. 



each other. The third zone, consisting of two groups merging with each 

 other, is located behind the attaching disc on a cone-shaped growth of 

 considerable diinensions (among both species about 0.008 - 0.012 x 0.012 - 

 0. 015 mm). This growth is exceedingly mobile and serves in some measure 

 for the regulation of the direction of the motion of the larva. This 

 cone is completely discarded as a unit with the shedding of the ciliary 

 epithelium when the larva becomes attached to the host. The larva carries 

 two groups of glands with well-developed ducts at the head end. There 

 are two pairs of large eyes (the anterior are somewhat smaller) with large 

 light-refracting lenses facing outside from the pigmented spot. The 

 pharynx lies behind the eyes, it is round and about 0. 015 mm in diameter; 

 the intestine is sac-shaped, weakly developed and poorly noticeable. 

 During the study of live subjects one can observe the lateral trunks of the 

 excretory system which give off numerous outgrOAvths and form a number 

 of anastomoses. Betrween the eyes and the anterior end of the pharynx 

 two transversal canals depart from the lateral trunks of the excretory 

 system. These canals merge in the middle and proceed toward the an- 

 terior end where they separate dichotomously. It has not been possible 



179 



