754 General Notes. 
EMBRYOLOGY .! 
OBSERVATIONS ON THE DEVELOPMENT OF CEPHALOPODS.’— 
In this memoir Mr. S. Watase deals very fully with the origin of 
the cells which give rise to the yolk membrane. With the excep- 
tion of Lankester, all authorities agree in describing the “ yolk 
membrane” as originating from the segmentation of the original 
germinal disk. As to the origin of the digestive tract, Kölliker 
and Bruce describe the digestive tract as continuous with the “yolk 
membrane.” Balfour and Lankester derive the “ mesenteron” from 
the lower layer of the mesoderm; Metschinikoff derives the major 
part of it from the ectoderm, while Ussow traces the whole diges- 
tive tract to the ectodermic involutions, . 
r. Watase’s conclusions are as follows in regard to these points: 
(1) The “ yolk membrane” is derived from the original germ disk; 
es it makes its appearance underneath the marginal zone of the 
germ disk, near to the junction of the intermediate zone; (3) the 
cells of the “yolk membrane” are irregular in outline, fusiform 1n 
cross-section, ameeboid in movement, each with one or more large 
nuclei; (4) with the growing edge of the blastoderm the under- 
lying “yolk membrane” keeps pace in growth with the area) 
germ disk, but never coming outside of the peripheral zone ; (5 
the “yolk membrane” grows at the same time from the margin to 
the centre of the disk, and in time it comes to completely separate 
0 
the epibolic gastrula; (7) hence Mr. Watase believes the “ yolk 
membrane” to be necessarily a true endoderm, and its sole repre 
ee re i Š an 
mic invaginations, that is, by prolongations of the proctodæum at 
stomodæum ; (9) at no period of the development does there wee 
any connection between the “yolk membrane” and the Bpi 
tract, and long before the absorption of the food yolk is comp 
the permanent digestive canal is formed ; (10) with = pen 
of which 
1 Edited by Prof. John A. Ryder, Univ. of Penna., Philadelphia. 
_? Studies from the Biological Laboratory of Johns Hopkins Univer- 
sity. Vol. IV., No. 4, pp. 163-181. June, 1888. 
