gf 7. es et ee Le NF ee eee 
182 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
most promising method of pursuing the investigation is that of 
sectioning ephippial females in various stages with the microtome. 
A preparation of soap was employed with partial success as a medium 
for embedding. 
Development of Daphnia. 
Although the careful researches of Claus and Grobben have added 
much to our otherwise rather meager knowledge of the development 
of the Cladocera, there still remain many interesting points, particu- 
larly with reference to the individual species, which merit careful 
study. 
The following observations relate to the single species D. scheffert 
which was available during a short stay in Leipzig. 
The winter eggs of D. schefferi are two in number and are lodged 
in the well known manner in an ephippium. 
The shape of these eggs is sharply ovoid, there being no distin- 
guishable difference between the two ends. The position in the 
ephippium is not, as might be expected, with the longer diameter 
parallel to the axis of the body, but the posterior end is slightly ele- 
vated. This is undoubtedly due to frequent elevation of the abdomen 
between the valves during the extrusion of the eggs. 
The color is dark green and the only protection as the egg leaves 
the ovary is a thick, tough shell which is at first so soft as to be sus- 
ceptible to pressure. It is thus reticulated, apparently through the 
Simple pressure of the walls of the ephippium. 
The length is 0.43 mm.; width 0.33 mm. in the average, though 
eggs were occasionally found of an elongated form, measuring 0.48, 
0.31 mm. The contents of the egg consist of spheres of greenish 
plasma of various sizes and fat or oil drops. These oil globules are 
not very numerous as compared with those of the summer eggs, and 
likewise never attain the dominant size seen in the latter. The various 
forms assumed by the plasma balls are perplexing but frequently result 
from the action of external agents. The cleavage stage was not 
seen, and if actual segmentation takes place, it must be inconspicuous 
as would be expected from the large quantity of yolk present. The 
differentiation of the blastoderm occurs very early, perhaps in the 
ovary itself, and the result is a tolerably uniform layer of prismatic 
cells. The egg now comes to a period of repose after the blastoderm 
has produced a second external envelope apparently by simple 
secretion. 
This envelope consists of a fine structureless membrane. The egg, 
under ordinary circumstances, remains dormant during the winter in 
this most favorable stage. The reason for which is evidently the fact 
