STBDCTUEE AND DEVELOPMENT OE EEISSNEE’s FIBEE. 43 
nucleus ” will prove to be sensory, and to be simply a part of 
that series of dorsally placed giant-cells which are such a 
conspicuous feature in the central nervous system of Cyclo- 
stomes and fishes. In support of this view I shall point out 
that, in Petromyzon fiuviatilis, the giant cells of the cord 
do not cease, as stated by Johnston for P, (Lampetra) 
wilder!, behind the commissura infima (’02, p. 5), but 
extend forwards almost to the cerebellum high up on the 
medulla on either side of the fourth ventricle. These in 
many instances project almost through the epeudymal 
epithelium into the ventricle, exactly as the cells of the 
“ Dachkern ” commonly project into the mesocoel. 
I find, also, a striking similarity in the staining reactions 
of the cells of the “Dachkern” and of the giant-cells of the 
cord in those forms where both are developed. Various 
observers, too, have noticed the failure either of the cells of 
the “Dachkern” or of the giant-cells of the cord to impregnate 
with Golgi’s method. Further, Sargent remarks that (in 
young Raia) many of the tectal reflex cells are to be seen 
“apparently undergoing atrophy and degeneration, showing 
all the stages in the process that have been observed in the 
atrophy of the dorsal giant-cells of the spinal cord” (’04, p. 
166). 
In Elasmobranchs, amongst others, the dorsal giant-cells of 
the spinal cord have been said to completely disappear 
during embryonic life (Beard, ’89, Studnicka, ’95b), whereas, 
as I shall describe in a subsequent paper, some, in the 
hinder part of the spinal cord, are to be found persistent in 
specimens of Raia six to eight inches long, and in adult dog- 
fish. Not only so, but in the latter at any rate they grow to 
an enormous size and become multinucleate. It is, however, 
not without significance that some of the cells of the “Dach- 
kern ” should be undergoing marked degenerative changes 
so pi’ecisely similar to, and at the same period in develop- 
ment as, many of the giant-cells of the cord. 
It is, I believe, now generally accepted that these giant- 
cells of the cord are sensory, and are derived from neuroblnsts 
