IRREGULAR CELLS IN SPINAL CORD OF FISHES 307 
The cytoplasm of the cells in most of the forms was homogene- 
ous. In the cell from the sandshark (fig. 7), however, there may 
be seen at the periphery a vacuole containing a fine granular 
precipitate. This is probably a secretion of the cell. Well- 
defined granular precipitate of secretion contained in definite 
vacuoles at the periphery of the cell was also seen in the shark- 
sucker. It has previously been pointed out that in the Dahl- 
gren cells of the skate such vacuoles containing fine precipitate 
are of common occurrence. These vacuoles often are outside of 
the cell in the neighboring tissues of the spinal cord. Granular 
material associated with the cells, but outside of them, has 
been noticed in the dogfish, flounder, menhaden, and possibly 
tautog. Another interesting feature in connection with the 
appearance of the cytoplasm of the Dahlgren cells is that it is 
often pierced by one or more capillaries (especially in the case 
of the shark-sucker), so that in cross-section the capillary with its 
endothelium and enclosed blood corpuscle appears to lie within the 
cytoplasm of the cell. 
In the case of the other fishes of the second group, the sting- 
ray (fig. 8), the dogfish, and torpedo-fish, the cells are larger, 
the volume of nuclear material relatively larger in comparison 
to the amount of cytoplasm and the nucleus more lobulated. 
The cells in these forms, indeed, almost make a series of transi- 
tion stages leading up to the third group. In general, it may be 
said that the Dahlgren cells are larger and their nuclei more highly 
branched in the elasmobranchs than in the teleosts or ganoids. 
The one notable exception to this rule is the summer flounder. 
In none of the cells of the second group were Nissl bodies seen, 
although in the neighboring muscle motor nerve-cells they could 
be clearly made out. 
The cells from the fishes of the second group, as arranged in 
figures | to 8, make an interesting comparison with the cells in 
embryo skates in various stages of development. The two series 
are very similar. In other words in the development of the 
complex type found in the adult skate simpler stages are passed 
through. ‘These simpler stages may be found in the adults of 
the fishes which have been placed in the second group. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 34, NO. 3 
