can fluctuate considerably. For instance, in D^ wegeneri Kulwiec this 

 ratio is approximately 1 to 5 and in D. vastator Nybelin 1 to 9, i- e. , 

 almost twice as long. 



The larva which has just emerged from the egg swims freely 

 (Fig. 138). It is covered with ciliary epithelium located in three zones 

 just as in Acolpenteron. The first zone^ consisting of two groups of ciliary 



0.01mm 



Fig. 137. Dactylogyrus vastator Nybelin, left egg is separated from the 

 uterus of the worm and has not yet been completely formed; the two re- 

 maining eggs with developing larvae were deposited by one individual. 

 (According to Bychowsky 1933). 



epithelium, lies at the anterior end of the body and extends posteriorly 

 approximately to the level of the posterior pair of eyes. Each of the groups 

 is located laterally, extending, however, to the ventral and dorsal sides 

 of the body, but they come in contact only at the anterior end during its 

 contraction. 



The second zone lies behind the pharynx approximately in the 

 middle of the body and its posterior edge is located at the level of the upper 

 ends of the edge hooks. This zone consists of two groups of epithelium 

 located along the sides of the body. The third zone of ciliary 



epithelium lies at the extreme posterior end of the body of the larva and 

 apparently originates from two groups of cells (Kulwiec, 1927, Table 21, 

 Fig. 2) mostly fused together. It is somewhat displaced to the dorsal 

 side and is located on a special growth of the body which is very mobile 

 and which disappears later. During attempts to count the number of 

 ciliary cells, it was possible to determine that in D^ intermedius it is 

 relatively large (compare with Polystoma, page 182 ); thus, in the anterior 

 zone there are more than 18 ciliary cells. At first the body of the free- 

 swimming larva is elongated in the shape of a cigar, its attaching disc is 



149 



