entire mass of larvae which were found at this tinne on the fishes were in 

 absolutely the same stage of development. Thus, the deposition of eggs 

 among these forms takes place extremely rapidly (see chapter on life 

 cycles, page 111). 



cells in the interior of the body somewhat above the attaching disc which 

 apparently play a role in the formation of the middle hooks. The latter 

 are incepted in their places alnnost simultaneously and descend to the disc 

 together (Fig. 167). However, certain differences are observed in the 

 tempo of their growth: the first pair grows somewhat faster and among 

 the mature animals it was slightly but distinctly larger than the second 

 pair. The nature and the sequence of the development of middle hooks 

 are the same as among Dactylogyrus (Fig. 168). The copulatory organ is 

 incepted in the shape of a pipe of almost the same shape and size as 

 among adult animals but with a weakly developed base which grows rather 

 slowly (Fig. 169). The time of inception of the copulatory organ coincides 

 with the beginning of the fornnation of the extensions of the second pair of 

 middle hooks. 



6. The development of Ancylodiscoides Yamaguti 



The genus Ancylodiscoides (Fig. 65), established in 1937 by 

 Yamaguti, pertains to Ancyrocephalinae and is characterized mainly by 

 the structure of the attaching apparatus, which consists of 14 very small 

 edge hooks and 2 pairs of middle hooks. The latter are of different sizes 

 and the interior offshoots of the large pair are equipped with supplementary 

 plates articulating with them (Fig. 170). There are four eyes. The in- 

 testinal trunks merge at the posterior end. The sex system (is equipped, 

 nobis) with a strongly developed chitinous copulatory organ and vaginal 



pipe (the latter is sometimes absent). 



They parasitize Siluridae and Bagridae. 



At the present time there is a number 



of materials (papers, nobis) about the 



development of the representatives of 

 aoiHM VV I ' h ^^^^ genus. Thus Siwak (Siwak, 1932) 



in a work dedicated to the description 

 Fig. 169. Protancyrocephalus of A. vistulensis Siwak from the gills 



strelkowi Bychowsky, stages of the European Silurus reproduces a 



of development of the copu- drawing of a free-swimming larva of 



latory organ. Explanation in this type and presents his observations 



text. on the development and further growth 



of the larvae. A. V. Gussew in 1948- 

 1949 hatched the free -swimming larvae of A. strelkowi Ackmerow and A. 

 varicus Ackmerow. Finally, during our work in the Delta of the Volga in 

 July, 1932 we sketched one of the later stages of development of ^ siluri 



// 



171 



