168 BULLETIN OF THE 



The third type is that of the large x cells, represented in Figure 28, 

 Plate III. These vary considerably in size and shape ; the mean longi- 

 tudinal diameter is 55 /x, the transverse 40 fx. The cell protoplasm 

 stains rather deeply, and is notably granular. These granules resolve 

 themselves in the nerve processes into fine lines. Each large ganglionic 

 cell contains a number of clear spaces, the paramitome, exactly similar 

 to those already described for cells of the second class ; and these are 

 often arranged concentrically, and more or less regularly along the 

 periphery of the cell. The single nucleus, 15 by 12 ^u. in diameter, is 

 usually found nearer the end of the cell from which the nerve fibre 

 emeiges, and, in contrast with those already described, is stained only 

 lightly. A nuclear membrane is very distinct, and there is one large 

 nucleolus 2-3 /x in diameter. In rare cases two smaller nucleoli were 

 found, never more. The nucleus also contains numerous fine granules 

 of chromatine, which are very distinct in the matrix, which remains 

 completely unstained. Xuclei of this class are not infrequently cres- 

 centic, with a clear space enclosed by the horns of the crescent, corre- 

 sponding exactly to such forms as are figured by Rhode ('87, Taf. IV. 

 Fig. 51 et at.). Although variable, these cells represent a more isolated 

 type than either of the other classes, and intermediate forms, especially 

 in nuclear appearance and structure, are rarely seen in the brain. 



An examination of the ventral nerve cord in transverse section shows 

 a preponderance of cells of the second class. The first class is poorly 

 represented, though the size of the plasmatic portion varies greatly in 

 different cells. Occasionally one finds cells which in their deep staining 

 and nuclear appearance recall the large cells of the brain. But meas- 

 urements showed one such cell to be only 24 by 30 fx and its nucleus 

 7 by 11 fx in diameter, dimensions which are far smaller than those of 

 the average of the large cells in the brain. These cells do not seem to 

 be regularly arranged in the ventral nerve cord, and no grouping could 

 be found which suggested metamerism. The peripheral nervous plexi 

 possess very few ganglionic elements, and these few are not reducible to 

 the types present in the central nervous system, for they are invariably 

 multipolar, and are situated at the crossing or branching of fibres. 



1 It is much better, for the sake of clearness in neurological terminology, to 

 keep the term "giant cells" (Riesenzellen) for the huge elements in the ner- 

 vous system of Nemertines, Annelids, et a/., as German writers have done, than, 

 with Shipley ('90, p. 16) and Andrews ('90, p. 424), to apply the term to such 

 cells as I have placed in the third class, to which the former are at most only re- 

 motely homologous. 



