Gland-Cells of Internal Secretion in Spinal Cord of Skates. 29 
SUMMARY. 
1. In the posterior portion of the spinal cord of the skate there are 
present large, irregular cells of peculiar structure. 
2. These cells are present in the anterior horn on each side of the 
central canal. 
3. There are about 600 in all in an animal of the species Raia ocellata. 
4. The nucleus of each cell is a lobular branching structure extending 
throughout the cell. The chromatin is scattered throughout the nu- 
cleus in the form of large granules. No definite plasmosome is present. 
5. The cytoplasm of a resting cell is homogeneous. In active stages, 
however, the cytoplasm is characterized by the appearance of small vac- 
uoles which often coalesce into larger ones. Secretion appears in these, 
and finally the contents of the vacuoles are discharged in the form of 
granules which persist in the tissues of the spinal cord for some time. 
6. This granular material is protein in character. It is not easily 
soluble. 
7. These cells develop from the same neuroblast tissue that gives rise 
to the muscle motor nerve-centers and electric motor nerve-centers. 
8. Cells homologous to them have been found in the spinal cord of 
torpedo, sting-ray, dog-fish, shark, goose-fish, gar-pike, and sword-fish ; 
not, however, in Fundulus nor in Necturus. 
9. The following theories as to the nature of these cells have been 
considered: (1) That they are nerve-cells; (2) that they represent 
parasitic or pathological conditions; (3) that they are phagocytes; 
(4) that they are gland-cells of internal secretion. The evidence, 
morphological and experimental, indicates that the cells are gland- 
cells of internal secretion. The experimental evidence consists in 
increase in volume of granular material following electrical and pilo- 
carpine stimulation of the spinal cord. No increase in volume of 
granular material follows atropine stimulation. 
10. The exact function of the granular secretion of these gland-cells 
is unknown. 
LITERATURE. 
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