STUDIES ON THE ECTOPAEASITIC TREMATODES OP JAP AX. 79 



obviously ganglionic cells can not be observed ; but in Microcotyh 

 sebastis there are two pairs of large polygonal cells in the ventro- 

 lateral portion of a cross-section passing through the anterior part of 

 the brain, which are provided with very large, vesicular nuclei with a 

 distinct membrane and containing each a single, large nucleolus and 

 numerous, weakly stained granules (probably chromatin). The proto- 

 plasm is finely granular and has no external membrane, so that the 

 cell-body becomes gradually fainter towards the periphery (PI. TV, 

 5). In Axine heterocerca (PI. VIII, fig. 2) also, there are some 

 cells of this kind of various sizes in the same region of the body. 

 In DicUdophora sessilis (PI. XI, figs. 1 & 2) the brain itself is entirely 

 free from cells of all sorts ; but at the root of the posterior nerves, 

 there are numerous cells of polygonal form with finely granular, 

 well-staining protoplasm, and with a nucleus containing one or more 

 nucleoli. These are undoubtedly nerve cells. Besides these, how- 

 ever, there are in this species two pairs of gigantic cells in that part 

 of the body which corresponds to whei'e the large cells already 

 mentioned ai*e found in Microcotyh sebastis. They are polygonal in 

 form, and the large vesicular nucleus, which contains, besides a single 

 large nucleolus, numerous small granules, is surrounded by a very 

 finely granular, well-staining protoplasm which is totally destitute of an 

 external membrane. Sometimes the protoplasm has seemed to be 

 drawn out into a faint process, and fibres to be given out from the peri- 

 phery of the nucleus (PI. XI, fig. 1, left side). I have described similar 

 cells in similar positions in Diplozoon^^ ; and I have no doubt that they 

 as well as those of Microcotyh and Axine are ganglionic cells. 



In Tristomwn, there are numei'ous ganglionic cells within the 

 brain as well as in the main nerves. The greater number of them are 



1). I. c. p. 171, and fig. 25. 



