221 



it is entirely absent, the karyoplasm appearing homogeneous through- 

 out (Fig. 6, a). This lighter area presents various and often peculiar 

 shapes, being sometimes crescentic (Fig. 6, b) and occasionally sending 

 out forked tongues toward the periphery of the nucleus. In some 

 preparations the place of this area is a clear space, and the karyo- 

 plasm can be seen to have shrunken away from the nucleolus at one 

 side, leaving the space in the form of a crescent. From the examin- 

 ation of a single cell like that shown in Fig. 8 a quite different inter- 

 pretation would be possible, namely, that the lighter area is the 

 nucleus and the darker substance a differentiated portion of the cyto- 

 plasm aggregated about the nucleus. The examination of several 

 hundred cells preserved and stained by a variety of methods shows, 

 however, that this is not the proper interpretation. 



The cytoplasm has a characteristic shining appearance, being 

 highly refractive. Under a 1 / lg in. oil -immersion lens it appears 

 finely granular. The granules are elongated their long axes being 

 parallel to the cell wall (Fig. 6). They are most conspicuous in the 

 larger dorsal end of the cell, gradually fading out toward the point 

 from which the axis cylinder arises. The cytoplasm occupies prin- 

 cipally the ventral part of the cell (Figs. 6, 8, 9, 10); but usually it 

 may be seen to form a peripheral layer around the dorsal side of the 

 nucleus (Figs. 6, 10). In cells having the forms of . those shown in 

 Fig. 4 the nucleus is approximately spherical 

 and lies in the dorsal part of the cell, the nil. 



cytoplasm having the appearance of having 

 been crowded ventrad (Figs. 6 a, 8). {^ ~^n 



Neurites. — As has already been stated, J 



the cells are in general unipolar, each one 

 giving off a large neurite which passes ven- n ^- " 

 trally into the cord (Fig. 3) The neurite 

 may pass directly ventrad or obliquely ventro- 

 cephalad or ventro-caudad , or again it may 

 run horizontally near the surface of the cord 

 for a distance equal to five or six times the 

 diameter of the cell before passing ventrad. 

 Rarely a neurite is seen to pass out laterally 

 from the cell and become lost in the gray 



Fig. 10. Giant cell. The nucleus (nl.) shows the chromatin net; the nucleolus 

 contains transparent granules. Camera drawing; obj. 7a, oc. 2, details with V 12 oil imm. 



