simplest forms and which has already been applied to Monogenoidea (see 



page 187 ). First of all, our data affirmed that the number of cells of 



ciliary epitheliuna annong larvae of Polystomatidae is constant as was 



supposed earlier and first determined by Ozaki (Ozaki, 1935b). Altogether 



the ciliary epithelium of the larvae of P. integerrimum consists of 55 cells. 



It is characteristic that the cells of the ciliary epithelium do not form a 



continual covering but each of them lies separately (lie in separate zones, 



nobis). The first zone of ciliary cells is located in front of the first pair 



of eyes and consists of 25 cells located (symmetrically in relation to the 



mesial line of the body) in two groups. The first group consists only of 



one cell which lies terminally or more often is slightly displaced to the 



dorsal side; the 18 cells of the second group are located on the ventral 



side as a belt completely encompassing that side of the body of the larva, 



whereas the remaining 6 cells of this group are located on the dorsal 



side with three on each side so that the basic part of the dorsal surface 



is deprived of ciliary epithelium. The second zone consists of 18 ciliary 



cells divided into two groups, of which the first lies approximately at the 



level of the middle of the pharynx and the second somewhat toward the 



front of the anterior end of the attaching disc. The first group has 6 cells p. 184 



located on the dorsal side, three on each side of the body so that the edge 



cells are easily visible from the ventral side of the larva. The first 



group of this zone consists of 12 cells lying symmetrically in a group of 



6 cells on the ventral and dorsal sides. Finally, in the third zone, 



12 cells lie on the dorsal side of the posterior half of the attaching disc 



somewhat away from its posterior end so that the 2 edge ones on each 



side are clearly visible from the ventral side when the larva is observed. 



In such a fashion 24 ciliary cells are located on the ventral side of the 



larva, while on the dorsal--30, and finally one cell lies terminally. 



Apparently such an unequal distribution of cells appears to be the reason 



for the peculiar swaying motion of the free -swimming larva. 



The head end of the larva is equipped with four groups of 

 glands. Four pigmented eyes of the larva with well-expressed lenses 

 are located somewhat in front of the pharynx. The digestive system is 

 rather powerfully developed. The pharynx is somewhat extended in 

 length (0. 04 x 0. 03D mm), it lies at the end of the first and the beginning 

 of the second third of the body. The intestinal tract emerges from it in 

 the form of a small esophagus. The intestinal tract is elongated, with 2 

 branches which merge in the end of the body. Between the 2 branches of 

 the intestine there is one, or more rarely, 2 anastomoses lying approxi- 

 mately in the middle part of the intestinal space. The excretory system 

 is well-developed. Its openings are located along the sides of the body 

 and on the dorsal side and somewhat behind the pharynx. There are also 

 small excretory bladders. The trunks of the excretory system, which 

 lead to the posterior and anterior ends of the body on each side, apparently 

 do not form transversal connecting canals. One must note that we our- 

 selves did not study the excretory system, and all the existing descriptions 



199 



