28 Papers from the Department of Marine Biology. 
shows that the animals can survive for some time at least without the 
secretion of these cells. More experiments must, however, be made 
before it can be said with certainty whether or not the cells are vital 
to the life of the skate. 
REGENERATION. 
One skate was collected which had at some time in its history lost the 
last 2 or 3 inches of its tail, only one little tail-fin being present instead 
of two. The skin had closed over the wound and grown together. 
Upon examining the end of the spinal cord it appeared that some regen- 
eration had taken place, the last sixteenth of an inch of the cord being 
minus the usual line of black pigment along the mid-dorsal line. Upon 
sectioning this region one of the gland-cells was found, but it was very 
small, being no larger than an ordinary nerve-cell. A few small gran- 
ules were also seen. It was concluded that this small cell represented 
an attempt at regeneration, probably having originated from the last 
normal cell—that is, the cell most posterior in position at the time of 
the injury. 
FUTURE LINES OF INVESTIGATION. 
Future investigation of this whole subject may be pursued very 
profitably in two directions. The first consists in a thorough compara- 
tive study. Undoubtedly the morphology of these cells in other forms 
of fishes, and perhaps in some of the higher vertebrates, will help to 
clear up their exact significance. It must be pointed out that the con- 
clusion that the cells are gland-cells applies only to the skate. The 
appearance of the cells in the other fishes studied does not warrant the 
same conclusion. The cells of the goose-fish, particularly, look unlike 
gland-cells and more like nerve-cells. It may prove to be of great 
evolutionary significance to trace out the steps by which nervous 
tissue has become modified and transformed to glandular tissue, as 
illustrated by the comparative morphology of these cells. Another 
promising line of investigation is to be found in experiments with 
extracts of the granular secretion. Unlike the secretion of other endo- 
crine organs, these granules are not readily soluble in water and alcohol, 
and it may not be easily possible to obtain a fairly pure extract. How- 
ever, if a satisfactory method of getting this is worked out, the results 
following administration of the extract to animals should prove to be 
of interest. The writer hopes to pursue both of these lines of investi- 
gation. 
