1894.] Embryology. 353 
ing, but unsuccessful, experiments recorded in addition to these of im- 
mediate value. The general result is that the blastopore begins to form 
below the equator of the egg, in the white region, and closes in by a 
peculiar overgrowth from the dorsal lip, so that we cannot speak of a 
real process of concrescence of two lateral areas. The embryo is, how- 
ever, formed along this region, that is upon what was the lower white 
side of the egg. 
Embryology of Cyclascornea.—Heinrich Stauffacher has 
recently (Jen. Zeit., II Heft, 1893, pp. 196-246) studied in consider- 
able detail the development and segmentation of the ova in Oyelas 
cornea L., in which the ova are developed in a single pair of follicles, 
the sperm in several pairs. The follicle is a simple tube lined with col- 
umar epithelium, surrounded by a homogeneous membrane. The 
primitive ova first appear as small spherical or elliptical cells next the 
membrane, among the bases of the cells of the follicle. The nucleus 
occupies almost the whole cell and has its chromatin rather uniformly 
distributed in the form of granules. As the ovum grows, it projects 
into the cavity of the follicle beyond the surrounding cells, but remains | 
attached to the membrane by a constantly narrowing stalk. The egg 
membrane is formed only over the free projecting portion ; the point 
of the ovum by which it is last attached by the stalk, persists as the 
micropyle. The ovum grows in part by the absorption of the surround- 
ing cells of the follicle. Two Centrosomes were found in the mature 
ovum. 
Stauffacher’s description of the earliest stages of segmentation does 
not differ widely from Ziegler’s account (Zeit. Wiss. Zoöl., Vol. 41). 
The egg divides into a small primary micromere and a large macio- 
mere. The former divides into right and left secondary micromeres, the 
latter into a second primary micromere and a macromere. This pro- 
cess is repeated, new primary micromeres being formed from the same 
side of the macromere, so that in these early stages, the secondary 
micromeres are arranged as right and left rows lying on the macromere- 
Bilateral symmetry is shown from the first. During the resting 
period after the formation of the first primary micromere, the proto- 
plasm of the micromere with its nucleus, becomes arranged around 
its free periphery, leaving a considerable cavity in the micromere next 
the macromere. As the second, third and fourth primary micromeres 
are formed, a cavity is similarly found in each. It disappears from 
each as the next primary micromere is formed, and is not present after 
the fourth. 
