corresponding bladder and extending posteriorly into the attaching disc. 

 They are connected by a transversal vessel in the posterior part of the 

 body. Each of these canals gives off one branch oriented forward which 

 terminates by one flame cell lying approximately in the middle between 

 the excretory bladder and the transversal vessel. The longitudinal canals 

 extend into the sucker and branch off into five vessels each in the latter. 

 These vessels terminate in flame cells. In addition to the large canals a 

 smaller one leading to the anterior end of the body emerges from each of 

 the excretory bladders. They unite in front of the buccal opening and form 



^ the middle canal which 



leads forward between the 

 . . eyes, beyond which it di- 



/ » • \ vides and branches off to 



%mt \ ^^® sides. Further, each 







Fig. 198. Benedenia melleni (MacCallum)^ 

 stages of the development of the larva. 

 Explanation in text. (According to Jahn 

 and Kuhn, 1932). 



p. 179 



Fig. 199. Benedenia 

 melleni (MacCallum), 

 diagram of the excretory 

 system of the free- 

 swimming larva. (Accord- 

 ing to Jahn and Kuhn, 1932). 



one of the branches bifurcates anteriorly and posteriorly and the branches 

 thus formed terminate in flame cells. There are four more flame cells in 

 the region of the buccal opening lying in front and behind the pharynx. Their 

 canals apparently branch off from the anterlolateral (canal, nobis). Thus, 

 the arrangement of the excretory ducts of the larva amounts to a "circular" 

 system with two lateral pores. The excretory system has a similar structure 

 in adult individuals. The larva is equipped with cilia in the anterior, middle 

 and posterior parts of the body. The anterior ciliary zone extends in front 

 of the first pair of eyes and the cilia practically cover the entire anterior 

 part of the body with the exception of the cephalic attaching organs. The 

 middle ciliary zone starts from the posterior end of the excretory bladders 

 and extends to the posterior end of the body (up to the disc) and covers the 

 sides and the lateral, dorsal and ventral surfaces with cilia. There are no 

 cilia in the middle of the dorsal or in the middle of the ventral surfaces. 

 The posterior ciliary zone occupies the lateral and dorsal surfaces of the 



193 



