of the body about 0.07 mm. The body is torpedo-shaped (Fig. 200), rather 

 narrowed at the level of the pharynx and in front of the attaching disc. The 

 latter is well-developed, it is sharply delineated from the rest of the body, 

 and rather larger than among B. melleni. Among free-swimming larvae it is 

 somewhat elongated in length. Its sizes are about 0. 09 - 0. 08 mm. The 

 head end is slightly flattened, the ducts of the head glands open into it by 

 bunches. The latter are rather powerfully developed and lie along the sides 

 of the body between the posterior pair of the eyes and the pharynx. There 

 are no "pad-shaped" sections from which, according to Jahn and Kuhn, 

 suckers are formed. In its structure the anterior end completely corre- 

 sponds to the one among Dactylogyridae, the only difference being that the 

 number of head ducts in B. derzhavini is larger and their size is more 

 considerable. The eyes, which have the usual location, are powerfully 



developed. The anterior pair is one 

 and one -half times smaller than the 

 posterior in diameter. The lenses 

 of the eyes are large and often of 

 oval form. The digestive system is 

 well-developed. The pharynx is 

 rounded and has a diameter of about 

 0. 03 mm; from it extends, clearly 

 visible in the live subjects, a sac- 

 shaped intestine which exceeds the 

 diameter of the pharynx by three to 

 four times. In such a fashion the 

 structure of the intestine in our 

 species sharply differs from the one 

 among B. melleni . The excretory 

 system is poorly studied. Two 

 powerful flask-shaped excretory 

 bladders, the dimensions of which 

 exceed the dianaeter of the pharynx, 

 depart from (open outside by, nobis ) 

 the dorsal pores. Two excretory 

 trunks emerge anteriorly and pos- 

 teriorly from the bladders (see note on page 178 ). These canals lie just 

 as they are pictured by Jahn and Kuhn in B. melleni with certain deviations 

 indicated on the drawing. We did not succeed in counting the number of 

 flame cells^ but it is considerable. The ciliary covering of the larva is 

 analogous to the one in B. melleni, but the description of Jahn and Kuhn 

 seems inaccurate to us. The anterior zone lies away from the anterior 

 end of the body at a certain distance and extends posteriorly to the level 

 of the first pair of eyes. It not only leaves the places of the eff erring ducts of 

 the head glands free, but it is also interrupted on the ventral and dorsal sides. 

 The middle zone begins below the excretory bladders and extends up to the 

 disc and apparently forms a break on the ventral side, whereas it extends 

 fully on the dorsal side. The third zone occupies the posterior half of the 



0.1 MM 



Fig. 200. Benedenia derzhavini 

 (Lajman), free -swimming larva. 



195 



