of the sides of the funnel-shaped buccal cavity, which is almost at the 

 very anterior end of the body. The pharynx is somewhat elongated 

 (0. 035 X 0. 032 mm) and lies behind the eyes. A long pipe -shaped in- 

 testine which forms small lateral outgrowths is located behind the 

 pharynx. The excretory system is poorly visible. Its openings are 

 located laterally at the place of the break between the first two ciliary 

 zones and the following ones. The excretory trvinks extend posteriorly, 

 curving in and out symmetrically along both sides of the body and enter, 

 branching off , into the attaching disc. Two snaaller trunks ,which extend 

 forward along the sides of the pharynx and extend above to the level of 

 the buccal suckers emerge from the two basic excretory trunks. The 

 attaching disc bears a pair of large hooks and 2 attaching clamps of the 

 usual form and structure (Fig. 233). The sizes of the clamps are about 

 0. 04 X 0. 05 mm. The hooks are of the same shape as among Discocotyle 

 sagittata (Leuckart). They are divided into the end hooks, strongly 



elongated and having a 

 weakly curved point, and 

 into a thin bending handle 

 which is about 2 to 2 1/2 

 times longer than the end 

 hook. The general length 

 of the hooks is 0. 07 to 

 0. 11 mm. We can ob- 

 serve in live larvae that 

 the points of these hooks 

 protrude outside 

 from the very moinent of 

 the emergence of the larva 

 from the egg. They move 

 very actively, not only 

 during the moments of the 

 settling of the larva, but 

 also during its swimming. 

 The edge hooks were 

 neither discovered by Zeller nor by us and it can be considered almost 

 certain that they are absent. This circumstance cannot cause special 

 astonishment because D. paradoxum represents a very specialized and 

 isolated species. After the attachment of the larva (diporpa) to the gills 

 of its host it loses the ciliary epithelium, begins to feed and undergoes 

 further changes. At this time a small sucker is formed on the ventral 

 side of the body, somewhat closer to the posterior than ariterior end, 

 while on the dorsal side correspondingly but still closer to the posterior 

 end of the body a small growth (Fig. 234 A) is also formed. At the same 

 time the other pairs of attaching clamps begin to be incepted in sequence. 

 Mostly around the moment of the inception of the second pair of clamps, 

 the larvae meet in pairs and unite, continuing further development to- 

 gether (Fig. 234 B). Often, however, one can observe that the junction 



0.05HM 



Fig. 233. Diplozoon paradoxum Nordmann, 

 attaching armature of the free-swimming 

 larva (somewhat flattened). 



203 



220 



