ON DIPLOZOON NIPPOXrCUM, N. SP. 165 



fragmentary pieces ii>* " Bügel, zahnfönnige Vorspriingf. Ki}ipen, 

 u. s. w." All the |)«)steri<^r suckers are of the same build ; but they 

 vary somewhat in size, the last pair being always smaller than the 

 anterior ones,^^ and the first pair very often smaller than the following 

 two pairs. Measurements on five individuals gave the average breadth 

 of the suckers as 0.093 mm.'' 



Besides the suckers just described, there is, on the dorsal side, a 

 pair of solid chitinous pieces (Fig. 6). Each piece consists of two 

 parts. The basal portion, to which a small bundle of muscle is 

 attached, is straight, and acts as a handle. To this is articulated a 

 hook-like piece, whose end alone sticks out fr(mi the surface of the 

 cuticula ; the handle as well as the other part of the hook lying in 

 the integument. The straight handle-like portion and the liook con- 

 stitute a single piece, and not two pieces as v. l^eneden'^' thinks. The 

 total average length of the piece is 0.072 mm. 



The anterior suckers are either round or egg-shaped, according 

 to the different states of contraction, and are situated right and left 

 at the entrance of the mouth. Like the posterior suckers, the walls 

 (Fig. 9) are composed of prismatic fibres placed at right angles to 

 the investing membrane, which lines the whole internal cavity, and 

 bounds the wall from the surrfMuiding mesenchyma. In cross-section, 

 the sucker is generally circular in outline. Each is provided with a 

 numlier of special muscles for the control of its uKnements in suction. 

 These muscles I have represented in Fig. 12, where there will be seen 

 three bundles coming from the dorsal side, two of which are attached 

 to the anterior border of the sucker, and the remaining one to the 



1) This faet must not be taken as proving that the hindermost pair is formed last. 



'J,i A corresponding- measurement on tlie European species «f about the same size gave the 

 average result as 0.144 mm. fort lie sucker, and 0.084 mm. for the tot;il length of the handle 

 and hook. 



3) P. J. V. Beneden— 1. c. p. 42. 



