Kulwiec and adds figures of the free -swimming larvae of D. crassus 



Kulweic and D. vastator Nybelin. Wilde (Wilde, 1937) gave a description 



and a number of figures of the development of _D. macrocanthus Wegener 



and in 1940 Groben (Groben) cites an analogous research to her work on 



D. vastator Nybelin and partially on'D. anchoratus (Dujardin) and D. 



macrocanthus Wegener. Certain material on the development of D. 



vastator Nybelin and D. solidus Ackmerow is given in the works of E. M. 



Lyman (1939 - 1951)'a^d O. N. Bauer (1948 - 1953). A collaborator of our 



laboratory A. V. Gussew in 1949 - 1950, who studied monogenetic trema- 



todes of Lake Hanka, secured during, the course of his works certain 



material on the development of 9 species of Dactylogyrus: D. curvicirrus, 



Achmerow; D. gussevi Achmerow, D. phoxini Malewizkaja, D^ eryth- p. 140 



oculteris Gussew, D. achmerowianus Gussew, D. contortus Gussew, 



D. obscurus Gussew, D. peltatus Gussew and D. leucisculus Gussew. 



Finally, during the period of 1927 - 1949 we studied the development of 



13 species D. anchoratus (Dujardin), D. intermedius Wegener, D. vastator 



Nybelin, D, wegeneri Kulwiec, _D. formosus Kulwiec, _D. cornu Linstow, 



D. fallax Wegener, D. crucifer Wegener, D. longicopula Bychowsky, D. 



solidus Achmerow, D. varicorhini Bychowsky, D. pulcher Bychowsky and 



D. modestus Bychowsky, with a varying degree of completeness. 



The adult Dactylogyrus (Fig. 5) is characterized by more or 

 less well-delineated attaching discs equipped with 14 edge hooks of approxi- 

 mately the same type as Acolpenteron andtwo middle hooks between which 

 lies a chitinous connecting plate. In approximately half of the species of 

 this genus there is, in addition, a supplementary chitinous plate located 

 between the middle hooks also but not directly connected with them, which 

 apparently serves for the attachment of musculature and the mechanical 

 fastening of the disc. The anterior end of the worms has four head growths 

 andtwo pairs of well-developed pigmented little eyes. The digestive 

 system consists of a powerful pharynx and smooth intestinal trunks 

 which merge at the posterior end of the body. It forms in such a fashion 

 an ellipsis inside of which the sex system lies. A powerful development of 

 chitinous elements of the copulatory apparatus is characteristic for this 

 genus and has important significance in systematics. For the most part 

 the eggs of Dactylogyrus (Fig. 137) are deposited to the bottom although 

 samples may delay themselves on the gills of the host. 



In normal conditions, embryonic development lasts from 2-1/2 

 to 10 days depending upon the tennperature of the water which surrounds 

 the egg (see page 92 ). The larva which has just emerged from the egg has 

 a length generally 1-1/2 times larger than the length of the egg. For in- 

 stance, in D. wegeneri Kulwiec the length of the egg is about 0. 070 mm, 

 whereas the length of the larva is about 0. 100 mm, correspondingly among 

 D. vastator Nybelin 0. 090 and 0. 125 mm and^. macracanthus Wegener-- 

 07075 and 0. 120 mm. The length of the larva in relation to the length of 

 the body of the adult worm varies greatly and the relationship between them p. 141 



148 



