4 C. M. CHILD 



apico-basal gradient can be demonstrated with any of the agents 

 mentioned above, especially after staining with neutral red, and 

 the same gradient appears in eggs placed in a thin layer of sea 

 water exposed to evaporation and so becoming increasingly 

 hypertonic. The most marked differences along the egg axis 

 in decoloration, swelling and disintegration which serve as indi- 

 cators of susceptibility, appear in HgCl2 and CUSO4. 



Figures 1 to 5 show some of the protoplasmic indications of 

 the gradient as they appear in HgCl2 m/500000. These eggs 

 remained in sea water for thirty minutes after fertilization, when 

 the first polar body was forming or had formed. Then they were 

 stained to a uniform red color in neutral red — five or ten minutes 

 being usually sufficient — and were then placed in the HgCU 

 solution. Swelling and increasing translucency soon began at 

 the apical or animal pole and were followed by decoloration of the 

 swollen region. Other regions of the eggs usually showed little 

 or no swelling, but the decoloration gradually progressed basip- 

 etally through the protoplasm. After two hours in HgCL the 

 eggs showed the forms indicated in figures 1 to 4. In many 

 the apical region, the region about the polar spindle has under- 

 gone marked swelling, is almost hyaline in appearance and pro- 

 trudes as a more or less sharply defined area from the egg surface 

 (figs. 1 and 2). In such cases this region usually contains a 

 mass so deeply stained with neutral red as to appear black or 

 blackish. This mass is the nucleus or chromatin, and perhaps 

 includes more or less of the spindle region. Occasionally two 

 masses appear, unquestionably the two groups of chromosomes 

 of the second polar spindle in anaphase. These black masses 

 decolorize much later than the cytoplasm of this region, which 

 at this time is usually completely decolorized. In the basipetal 

 direction a decoloration gradient appears, from complete de- 

 coloration apically through all gradations of color to deep red 

 basally. 



In other eggs (figs. 3 and 4) the apical swelling is less sharply 

 defined and the black mass is less distinct or not visible. These 

 differences are doubtless associated with different stages of 

 maturation. In eggs like figures 3 and 4, the apical region is 



