468 BULLETIN OF THE 



ous in the lateral portions of the cord. Each part also contains nerve 

 fibrillse, and the relation of the ganglion cells to each appears to be the 

 same. 



There are, moreover, ganglion cells in the ventral nerve cord ; they may 

 be conveniently treated of in two groups, which correspond in general 

 to those of the brain. The first are simple nervous nuclei, distinguished 

 from the nuclei of the surrounding connective tissue especially by the 

 intensity with which they take up stains. They are small oval nuclei, 

 measuring 4-5 /x by 6-8 /x in diameter, and possessing a prominent nu- 

 clear membrane, but not provided with any appreciable amount of sur- 

 rounding protoplasm. They are found along the dividing lines between 

 the areas of the cord (Plate VIII. Fig. 101) and also on the external 

 boundary of the latter, usually closely crowded together ; in cross sec- 

 tions they appear as a single or double row ; in longitudinal sections 

 they are collected into a certain area (Fig. 97). They are about equally 

 distributed throughout the length of the cord, and produce the dark 

 dotted rows seen on the ventral line in the living animal (Fig. 7). 



The large cells of the ventral cord form the second class, and in many 

 cases are equal in size to those of the brain. Though not plentiful, 

 they are scattered along the whole length of the cord. I was unable to 

 find, however, any regularity of distribution, since the interspaces vary 

 considerably in extent. Furthermore, they are not plainly paired except 

 in rare cases. Usually the successive cells are separated from one another 

 by a distance equal to the thickness of ten, or even twenty, cross sections 

 (100 to 200 /x). Biirger (p. 641) has described these cells under the 

 name of median cells. I do not think that they begin, as he maintains, in 

 the brain ; but I agree with him in regarding them as unpaired. These 

 big cells are ordinarily found wedged in between the two lateral areas 

 and immediately below the ventral portion of the cord (Plate VIII. 

 Fig. 101). So far as I have seen, these cells possess each but a single 

 process, which passes dorsad between the median and one of the lateral 

 areas, but its ultimate fate I was unable to determine. Rarely one finds 

 a large cell below the lateral area on one side or the other. In this case 

 the nucleus is much flattened dorsoventrally. Biirger regards these 

 cells as bipolar. I have seen appearances such as he represents in his 

 Figure 13, but do not regard this as decisive, since the two processes are 

 not shown, so that, while I have no positive contradictory evidence, I 

 am also unable to confirm his statement. 



The form of the ventral nerve cord may be much altered by collapse 

 of the body, which flattens the cord between the two lateral muscular 



