54S 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
or retractor profundus ; the other three muscles of this fin are developed 
from cells which have arisen from the somatopleure, and perhaps, also, 
from the sclerotome. This condition seems to be intermediate between 
what obtains in Elasmobrauchs and Amphibians. The pectoral fin is 
derived entirely from somatopleuric cells. The author defers till the 
completion of further inquiries the full discussion of the meaning of 
this diversity in the origin of the muscle. 
Yolk-nucleus in Cymatogaster aggregatus.* — Mr. J. W. Hubbard 
has made a study of the compact irregular mass of granules which goes 
by this name, and is found in the yolk of the egg of certain animals. 
He comes to the conclusion that it originates from the nucleus soon 
after the cell becomes fully differentiated as an egg. It constantly 
moves towards the endodermic pole, where it is situated at maturity, 
and during later stages ; it is capable of growing to a considerable size, 
and has a definite chemical composition. It remains in the egg until the 
closing of the blastopore, when it breaks up and disappears in the yolks. 
It is found in the eggs of many animals, and has been described as part 
of the male cell. 
Development of the Selachian Head.! — Prof. C. K. Hoffmann finds 
that the nine head-somites described twelve years ago by van Wijhe in 
Scyllium and Pristiurus are to be seen very clearly in Acanthias , where, 
however, there are ten, the first trunk-segment (of van Wijhe) here 
taking part in forming the head. The segmental cerebral nerves .and 
the dorsal spinal nerves are segmental outgrowths of precisely similar 
nature. Hoffmann gives the following table : — 
Somite. 
Ventral Branches. 
Dorsal Branches. 
1 
M. rectus superior, in- 
ferior, interims and 
obliquus inferior. 
Oculomotor. 
Ophthalmicus profundus 
with van Wijhe’s 
ciliary ganglion. 
2 
M. obliquus superior. 
Trochlear (?) 
Trigeminus with its 
ganglion. 
3 
M. rectus externus. 
Abducens. 
Facial (acustico - faci- 
alis) with its ganglion. 
4 
No muscles 
0 . 
Rudimentary ganglion 
aborts. 
5 
55 
0 . 
j Glossopharyngeal with 
i its ganglion. 
g 
Transitory embryonic 
muscle- fibres. 
Not found. 
Anterior part of vagus 
and vagus ganglion. 
7 
Most anterior part of 
Embryonic only, aborts 
Posterior part of vagus 
the great longitudinal 
muscle. 
very early. 
and vagus ganglion. 
8 
55 55 
Well developed in em- 
bryo, aborts. 
; Very rudimentary, tran- 
sitory ganglion. 
9 
” 
Strong branch, persists, 
innervates head part 
of the great longitu- 
dinal muscle. 
Rudimentary ganglion 
aborts. 
10 
95 55 
And also the most an- 
terior part of the 
sternohyoid. 
As above. 
Ganglion persists, but 
seems to fuse with 
the first spinal gan- 
glion. 
* Proc. Amer. Phil. Soc., xxxiii. (1894) pp. 74-83 (3 pis.), 
t Anat. Anzeig., ix. (1894) pp. 638-53 (5 figs.). 
