its effering openings, located along the sides of the body, are somewhat dis- 

 placed toward the dorsal side, and are located at the level of the beginning 

 of the second zone of ciliary covering. The structure of the excretory 

 system was not followed through by us but it is completely evident that its 

 longitudinal trunks are doubled on each side. Immediately upon its 

 emergence from the egg, the attaching disc of the larva is well-developed 

 and separated from the body, and all its edges are drawn toward the middle, 

 and at that time it is incapable of functioning. The armature of the attaching 

 disc (Fig. 194) consists of 14 edge hooks and 3 pairs of middle hooks of p. 



different shapes and sizes just as among adult worms. The attaching disc 

 bears a third zone of ciliary epitheliurn which starts somewhat at the front 

 of the middle of the disc and terminates at its posterior end. The attaching 

 armature deserves special description. The edge hooks have uniformly 



straight handles and a connparatively power- 

 ful transversal growth of the terminal little 

 hook. Their sizes are more or less the same, 

 their length fluctuates from 0. 019 - 0. 021 

 mm iust as among adult individuals. The 

 first pair of middle hooks whic . is located 

 near the lower posterior edge of the disc, 

 has the shape of the middle hooks of Dac- 

 tylogyrus which are just completing the 



175 



01 MM 



! 



'^^^ 



Fig. 193. Nitzschia 

 sturionis (Abildgaard), 

 free -swimming larva. 



X 



0.01mm 



^ 



Fig. 194. Nitzschia sturionis (Abildgaard), 

 attaching armature of a free -swimming larva. 



growth of the basal part. Their sizes are about 0. 03 mm. The second 

 pair is located behind the first somewhat away from the center of the 

 attaching disc. In its shape it is an elongated plate with an obliquely- 

 growing upper edge and slightly curved lower edge ending in a somewhat 

 obtuse, rounded "point. " The sizes of the second pair are considerably 

 larger-- 0.048 - 0.050 mm. Finally, the third pair, located almost in the 

 center of the disc of the larva, have the shape of hooks with a slightly 

 widening basal part and with an almost straightened point and lateral off- 

 shoot which lies between the point and the basal part and has a somewhat 

 curved and free end which is directed toward the same side as the point. 



189 



