Gland-Cells of Internal Secretion in Spinal Cord of Skates. 5 
The electric organs of Raza ocellata extend throughout the tail, one 
on each side of the vertebral column. The anterior limit is about at 
the level of the thirty-third vertebra, or just anterior to the insertion of 
the pelvic fins. The posterior limit is the extreme tip of the tail. In 
the adult skate there are about 120 vertebree. Sections of the spinal 
cord were taken at various levels, as indicated by the shaded regions 
in text-figure 1. As a result, it was found that the cells in question 
were present in the spinal cord only from the level of the sixty-fourth 
vertebra to the tip of the tail... They do not, therefore, correspond in 
anterior-posterior distribution with the extent of the electric organs. 
They are situated opposite the caudal portion only of the electric 
organs. Any explanation of the function of these cells must take into 
account their peculiar distribution in the posterior part of the spinal 
cord only. 
The cells were found to vary in frequency in different parts of the 
spinal cord. Counts were made of the number of cells in each of the 
regions indicated in the figure, and a calculation of the number of cells 
per millimeter was made in each case. These results are summed up 
in table 1. The cells are seen to be most numerous near the tip of the 
tail in the region of the two little tail-fins. No arrangement of the cells 
corresponding to the segmental structure of the tail was apparent. A 
calculation of the total number of these cells showed that there were 
about 600. It is interesting to compare this with the number of elec- 
troplaxes in the electric organs of a large skate—20,000, as estimated 
by Ewart. 
MORPHOLOGY. 
A typical cross-section of the spinal cord of Raia ocellata in the region 
of these large cells is shown in plate 1, figure 1. The spinal cord is 
enveloped by the meninx primitiva, which carries the blood-vessels. 
The spinal vein is present on the dorsal side and the spinal artery on 
the ventral side. The central canal is situated more or less ventrally. 
The cells are found on each side of the central canal, lying on the ante- 
rior edgeof the graymatter. In this same section may be seen a nerve- 
cell, probably an electric motor nerve-cell. 
One of the most striking things about these remarkable cells is their 
great size. In bulk they average about 20 times the volume of the 
muscle nerve-cells. If they were nerve-cells they would be among the 
largest nerve-cells known. They are very irregular in shape, but may 
be described as somewhat elongated and slightly flattened cells aver- 
aging in Rava punctata about 300 mm. long, 200 mm. wide, and 176 mm. 
thick. The greater length lies in an anterior-posterior position in the 
cord, the width is lateral, and the thickness is dorso-ventral. These 
measurements do not take into account large local irregularities in the 
1The anterior limit varies somewhat in the different species of skates. In Raia levis and Raia 
punctata it is a few vertebre farther forward. 
