KOFOID: DEVELOPMENT OF LIMAX. 45 
distant, i. e. the first, being tho larger. In stained preparations the 
larger ono often contains a distinct nucleus with nuclear membrane and 
chromatic granules (Plate IIT. Figs, 20, 21). In the case figured here 
the two globules are closely applied to the surface of the egg. In the 
majority of instances, however, they lie at some distance from the egg in 
the albumen, and in the living egg often seem to have no connection 
whatever with the vitelline surface. Thus it happens that the polar 
globules are removed with the albumen in by far the larger part of the 
eggs shelled. A phenomenon observed occasionally in the later stages of 
the living egg is the increase in size of one of the polar globules and its 
subsequent collapse (Plate I. Figs. 9-11). In one case the globule 
reached a diameter half that of the egg itself. "This is apparently 
caused by the absorption of fluid from the albumen, and in the case 
noted was followed by a collapse and a return to the normal size and 
hape. The eggs of Agriolimax agrestis vary a great deal in size, the 
limits being from 80 u to 160 u in diameter. The average size-is about 
100-110 u. 
A. Orientation of the Embryo. 
In my treatment of the subject the orientation employed by Wil- 
son (92), Conklin (92) and Heymons (93) is followed. The first 
cleavage plane is transverse, the second sagittal, in relation to the future 
embryo. The polar globules are dorsal, the macromeres are ventral. 
This does not, however, distinguish the anterior and posterior poles, and 
I know of no way in which they can with certainty be determined in 
Limax. The cells of tho two ends are equal in size, generally, and when 
slight differences can be detected on careful measurement, it is impossible 
to follow these differences during the protean phases of cleavage that 
intervene between the two-cell stage and the appearance of the first 
mesoderm cell, marking the posterior pole. Inasmuch as the mesoderm 
cell (4^?) comes from the left posterior quadrant, and is itself quite & 
large cell, while its sister cell (471) doesnot seem to be much smaller 
than other members of its quartet, I have al ways placed the larger of the 
two touching quadrants of the basal quartet in tho position left posterior, 
rather than right anterior. I have been compelled to orient arbitrarily 
in many casos, when no difference in size could be deteoted, choosing 
one of the two positions 180° apart. In choosing tho larger cell I havo 
not followed the type of Umbrella, where without doubt the mesoderm 
comes from the smaller of the two cells in contact at the ventral cross 
furrow. 
