182 GEOL. AND NAT. HIST. SUKYEY 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 Gladocera, 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. schcefferi 

 which was available during a short stay in Leipzig. 



The winter eggs of D. sch(€^eri are two in number and are lodged 

 in the well known manner in an ephij)pium. 



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 

 l)etween 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 jiresent. 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 Qgg, 

 under ordinary circumstances, remains dormant during the winter in 

 this most favorable stage. The reason for which is evidently the fact 



