On Stichocotyle nephropis CiinniiiRlnun, a para.site of the American lobster. 473 



also one may be fouud which has two filaments passing from it in 

 opposite directions. The presence of these fibres, taken in connection 

 with the absence of cells having more clearly marked ganglionic 

 characteristics, furnishes sufficient evidence for considering the cells in 

 question ganglionic. There is, however, no aggregation of a con- 

 siderable mass of such cells in any one region, and they seem to be 

 only a little more numerous at the anterior end about the supra- 

 oesophageal commissure than along other portions of the nerve tracts. 



In the living worm studied under the compressor, there could be 

 seen very near the anterior end, in the position indicated by an 

 asterisk (*) in PI. 30, Fig. 19, numerous cells which appeared espe- 

 cially distinct, and whose form could be made out very clearly. Several 

 of these cells are represented in PI. 29, Fig. 8. Processes could be 

 traced from certain of them very clearly, and their appearance seems 

 to indicate that they are ganglionic cells. In sections, however, I am 

 unable to make out any difference between the cells of this region 

 and those in the other portions of the nervous system. That they 

 appeared so much more distinct here than elsewhere, was probably 

 due merely to the better conditions for observing them presented in 

 this part of the body. 



The parts of this system which Cunningham observed and de- 

 scribed were the transverse commissure and the rudiments of the 

 lateral nerves. Concerning the former, he says: "the fibrils of which 

 it is composed are extremely minute, and the whole tract is destitute 

 of nuclei." This he thinks "may represent the cerebral ganglion". 



Sense Organs. 



I shall describe as sense organs, certain structures observed 

 chiefly upon the ventral surface of the animal, and more abundantly 

 present near the anterior end. By far the greater number are found 

 within the cavities of the suckers. They are represented in PI. 30, 

 Figs. 13 and 14, and consist essentially of a fine filament which ex- 

 tends out through a distinct opening in the cuticula and ends free at 

 the exterior. Around the outer end of the pore the cuticula shows 

 a slight annular thickening. The filament, which occupies the centre 

 of the pore, may be traced inward through the muscle layers and 

 frequently may be followed for some distance through the parenchyma. 

 The outer free end of the fibre appears to be slightly thicker than 

 liie deeper portion lying in the cuticula. 



ZocO. Jahrb. Vlll. Abth. I Morph. gj^ 



