12 Papers from the Department of Marine Biology. 
It should be noted that the goose-fish is a teleost, whereas the skate, 
dog-fish, shark, torpedo, and sting-ray are elasmobranchs. Differ- 
ences in structure should therefore be expected. It is possible, how- 
ever, that these cells of the goose-fish are not homologous with the cells 
of the other fishes, although the fact that they are found in the posterior 
end of the spinal cord, just as are the other cells, makes it probable that 
they are homologues. At any rate, they certainly appear to represent 
a transitional stage between a nerve-cell and the highly differentiated 
cell of the skate. The evidence gathered from the study of the histo- 
genesis of the cell of the skate indicated that the cell might be regarded 
as a transformed nerve-cell. The morphology of these cells of the 
goose-fish, because of their resemblance to nerve-cells, lends support to 
this view. 
GLAND-CELL HYPOTHESIS. 
Assuming, then, that these large, peculiar cells of the skate are trans- 
formed nerve-tissue, the question at once arises as to what their pres- 
ent function is. The cytoplasm of the cells seems to undergo vacuola- 
tion and partial liquefaction, with the production of some precipitate 
and granular material. This, of course, suggests glandular activity. 
The granules may represent some specific secretion that is being pro- 
duced by the cells. The granules, after they have been manufactured 
and discharged, are not at once absorbed by the blood, but seem to 
persist in the tissues for some time. Most of them make their way 
down past the central canal toward the ventral side of the spinal cord. 
It is not known what causes most of the granules to gather in this region. 
Perhaps gravity pulls them in this ventral direction, or the movements 
of the neurolymph. Just ventral to the central canal a network of 
blood-vessels may often be seen. Here most of the granules are prob- 
ably absorbed. 
The whole process seems to indicate that these large cells are gland- 
cells of internal secretion. That such glands should be located in the 
anterior horn of the spinal cord seems to be remarkable; yet we know 
that other parts of the central nervous system have become profoundly 
modified. At various points in the brains of vertebrates are found 
places where the wall has been invaginated into long branching and 
anastomosing tubes of simple epithelium showing glandular activity. 
Blood-vessels have followed these tubes in and occupy their centers so 
that only a single layer of epithelium separates blood and brain fluids. 
Through this layer of epithelium substances are probably removed from, 
or passed into, the brain-cavity fluids. These structures are choroid 
plexuses. 
The pituitary body is another well-known example of the way in 
which nerve-tissue may become modified. As this is also one of the 
endocrine organs, or glands of internal secretion, its structure is of 
