expressed handle; their length is very insignificant- -about 0. 01 mm. 

 Among adult forms the sizes of the edge hooks are the same and conse- 

 quently no growth is observed among the latter in the'post-embryonic 

 period. Further development has not been followed through. The middle 



hooks of adult worms 

 are more or less of 

 the same sizes (Fig. 

 156); apparently the 

 ventral pair is in- 

 cepted first. In spite 

 of the fact that this 

 species is encountered 

 both in marine and 

 fresh water the develop- 

 ment of the eggs ap- 

 parently takes place 

 only in sea water, for 

 our attempts to 

 obtain larvae in fresh 

 water were not 

 successful. 



afl/M" 



Fig. 155. Ancyroce- 

 phalus (s.lat.) 



vanbenedeni (Parona 

 and Perugia), free- 

 swimming larva. 



Fig. 154. Ancyrocephalus 

 (s. lat. ) cruciatus Wedl. , 



adult worm from the gills 

 of Misgurnus fossilis(L,. ) 

 from the region of Peterhof 

 (Leningrad region). 



at an air temperature 



Ancyrocephalus (s. lat. ) mogurndae 

 (Yamaguti). Certain data concerning the 

 development of this species, discovered in Lake 

 Hanka in 1948-1949 on the gills of Sineperca 

 chua-tsi (Bas. ) are reproduced in the works 

 of A. V. Gussew (1955). He writes: "The 

 development continued about 3 days (65 hours) 

 on the first day of about 27° centigrade, the 



second--2lO to 26°, and the third--180 to 22°. The larva has a length of 

 about 0. 06 and a width of about 0.02 mm, it has 4 little eyes with little 

 lenses, is equipped with three zones of cilia, on the anterior end, along 

 the sides of the equatorial region and on the posterior (the latter is some- 

 what displaced toward the dorsal side). The attaching disc is closed. 

 Its armature (Fig. 157--B. B. ) consists of 7 pairs of edge hooks with 

 lengths of about 0.015 - 0. 017 mm. There are no traces of the middle 

 hooks. " In addition to that A. V. Gussew indicates that, "that on the gills 

 of the perch-bass ( Sineperca --B.B. ) one immature individual with a 

 length of 0. 34 rmn and a width of 0. 09 mm and with fully developed middle 

 hooks which have the same common length--0, 048 mm and the point 0. 019 rnm- 

 was found. The ventral connecting plate is still tender, 0. 005 x 0. 042 mm. 

 The dorsal connecting plate is very thin and apparently is incepted after 

 the ventral one during the development (just as the dorsal hooks), its sizes 

 are 0. 002 x 0. 055 mm. The copulatory organ and the vaginal armature 



165 



