edge hooks and 2 pairs of middle hooks of which one pair is larger. The 

 sizes of edge hooks do not change in the process of further development 

 of the larva and remain about 0. 03 mm during the entire life. The 

 smallest pair of middle hooks in the larva is 0. 035 mm and grows among 

 adult worms up to 0. 065 mm. Finally, the larger pair changes its sizes 

 from 0. 035 to 0. 12 mm. The fate of the larva which reaches the buccal 

 cavity of its host where the adult worms live is poorly studied; however, 

 in general traits its development apparently is analogous to that of Poly- 

 stoma (Fig. 208). 



18. The development of Diplorchis Ozaki 



The genus Diplorchis is also close to that of Polystoma but 

 differs by simple unbranched intestinal trunks, the presence of 2 testes, 

 and by the very powerful development of the uterus which extends pos- 

 teriorly to the attaching disc, filling the middle part of the body of the 

 worm almost fully, and almost completely displacing the parenchyma and 

 the vitellaria beyond the intestinal trunks. 



Ozaki (Ozaki, 1935b) worked on the development of D. ranae 

 Ozaki. He observed the deposition of eggs and also gave a good description 

 of the free-swimming larva. The eggs of D. ranae begin to develop in the 

 uterus of the parent individual. The eggs which are deposited contain 

 fully formed larvae (Fig. 209). The free-swimming larva which emerges 

 from the egg which is already in the water has a cigar-shaped, elongated 

 form (Fig. 210). Its length is 0. 24 - 0. 28 mm and its maximum width is 

 about 0. 08-0.1 mm. Its widest part is between the anterior end and the 

 pharynx; its anterior end is rounded, the attaching disc is well-delineated. 

 The ciliary covering of the larva of D. ranae (Fig. 211) was studied by 

 Ozaki by means of the silver impregnation technique. Thus, the precise 

 distribution and numbers of ciliary cells was clarified. Their total 

 number is 59. The cells are distributed in 5 groups lying symmetrically 

 on the ventral and dorsal surfaces and extending to the lateral edges. The 

 first group consists of one cell on the anterior, terminal end of the body 

 of the larva. The second consists of 26 cells located in a continuous mass 

 on the ventral surface of the larva fronn the buccal opening posterior to the 

 first half of the pharynx. The third group is located at the level of the 

 posterior edge of the pharynx and extends somewhat behind. It consists of 

 3 pairs of cells along the sides of the body of the larva. The fourth group 

 is located near the posterior end of the body and consists of 12 cells 

 forming a little belt along the dorsal side and the edges of the body and 

 extending only slightly onto the ventral surface. Finally the fifth group 

 consisting of 14 cells is located on the sides and the dorsal surface of 

 the posterior half of the attaching disc. Comparing the ciliary covering 

 of D. ranae with that of Polystoma integerrimum we see an almost 



203 



