2IO EDWIN G. CONKLIN. 



are formed is at this stage rich in yolk and is slate-gray 

 in color. 



After the clear and the yellow substances have collected at the 

 lower pole the sperm nucleus and aster move toward one side of 

 the egg which future development shows to be the posterior 

 pole ; the clear and yellow substances are also drawn over to 

 this side of the egg and in such a manner that the yellow cap is 

 transformed into a superficial band or crescent which lies just 

 below the equator of the egg on the posterior side, its arms ex- 

 tending forward on each side about half way around the egg 

 (Photos 3 and 4). Owing, perhaps, to the way in which this 

 crescent is formed from the cap of yellow protoplasm its ventral 

 border is sharper and its substance is of a deeper yellow than 

 the dorsal border. At the middle of the yellow crescent is a 

 small area of clear protoplasm which first gathers around the 

 sperm as it enters the egg and which afterward lies at the middle 

 of the crescent throughout the entire development ; this clear 

 protoplasm is seen in profile at the middle of the crescent in 

 Photo 3. 



The movement of the protoplasm to the posterior pole is ap- 

 parently initiated by the movement of the sperm nucleus and 

 aster to this pole ; here the sperm aster divides giving rise to the 

 amphiaster and here the two germ nuclei meet. The axis of 

 elongation of the amphiaster is always at right angles to the axis 

 which connects the animal and vegetal poles while its middle 

 lies in the plane of the first cleavage and in the median plane of 

 the embryo. The amphiaster lies beneath the yellow crescent 

 and some distance from the surface of the egg and the long axes 

 of the two coincide. In Photo 4 the clear line in the middle of 

 the crescent is the amphiaster seen through the superficial layer 

 of the crescent. It is probable that there is some causal connec- 

 tion between the elongation of the amphiaster and the formation 

 of the crescent. 



The clear protoplasm which also moves to the posterior pole 

 along with the yellow is chiefly withdrawn from the surface and 

 aggregated around the sperm nucleus and aster, though a por- 

 tion of it comes to the surface just above (ventral to) the crescent 

 (Photo 3). As the time for the first cleavage approaches the 



