on the anterior end of the body of the larva, two on its sides, the right and 

 the left, somewhat behind the pharynx, and finally the last group lies on the 

 posterior end of the body. The larva has two pairs of well-developed 

 pigmented little eyes lying in front of the pharynx. The little eyes are 

 equipped with light-refracting lenses located laterally. The little eyes of 



0.05mm 



Fig. 135. Acolpenteron catostomi 

 Fischthal and Allison, egg. 

 (According to Fischthal and Allison, 

 1941.) 



cw«« 



Fig. 136. Acolpenteron catostomi 

 Fischthal and Allison, free- 

 swimming larva. (According to 

 Fischthal and Allison, 1941. ) 



the anterior pair are 0. 006 mm in diameter, whereas the sizes of the pos- 

 terior--0. 008 x 0. 010 mm. Very frail edge hooks, about 0. 019 mm in 

 length, are located on the cup-shaped (?) attaching disc. Their number 

 is 14, just as among the adults. 



Further development is not described but is sufficiently 



evident. 



2. Development of Dactylogyrus Diesing 



The development of the worms of the genus Dactylogyrus was 

 studied by a number of authors. The first data on the biology of the develop- 

 ment and reproduction of eggs with the developing larvae of JD. vastator 

 Nybelin were given by Nybelin in his work of 1925. Later, in two of her 

 works, Kulwiec (Kulwiec, 1927, 1929) describes the development of D. 

 anchoratus (Dujardin), D. crassus Kulwiec and_D. vastator Nybelin, 

 separate stages of development of D. formosus Kulwiec andJD. wegneri 



147 



