EFFECT OF LACK OF OXYGEN. 149 



which were subjected to hydrogen immediately after fertilization 

 is in the first division plane sometimes coming in so as to divide 

 the egg into two slightly unequal cells. In most experiments, 

 the eggs developed into normal swimming larvae next morning. 



Eggs subjected to hydrogen at any later stage of development 

 up to the formation of the metaphase spindle behave similarly 

 to those described, and I have tried every stage. The astral 

 rays gradually disappear under hydrogen, leaving the egg quite 

 homogeneous; the eggs may become crenulated and irregular 

 especially in the early stages. But when oxygen is admitted, 

 the astral rays reappear and the eggs divide and develop normally 

 except for the occasional unequal division of the first two cells. 

 When the eggs are perfectly clear, the mitotic figure always 

 reappears when oxygen is admitted in exactly the same phase and 

 position in which it disappeared when oxygen was taken away. 



When the eggs are kept without oxygen while in the full 

 metaphase, in some cases the fibers become indistinct in about 

 half an hour, but usually they remain distinct for an hour or 

 more; in some cases the astral fibers have persisted longer than 

 two hours. After the fibers disappear, the eggs become almost 

 homogeneous, with perhaps a few darker areas (Fig. 7). W'hen 

 the eggs, stained in methylene blue are becoming decolorized by 

 lack of oxygen, the blue remains last in the granules among the 

 astral rays. This region is also a little more blue in the normal 

 eggs stained in methylene blue than elsewhere, and is especially 

 so in subsequent cleavages. In the very granular eggs of 

 Sphserechinus granularis, the region around the spindle and 

 asters is very blue while the periphery may be quite colorless. 



When oxygen is admitted to the eggs which have been in a 

 hydrogen atmosphere during the metaphase, the asters may 

 reappear in the course of an hour in the same place where they 

 disappeared (Fig. 8). In many cases, however, the mitotic 

 figure assumes a peculiar appearance, a decided white streak 

 running between the two asters and the astropheres are elongated 

 in one axis (Figs. 19, 24). The white streak gradually disappears 

 (Figs. 20, 21, 25, 26). 



The eggs which have been subjected to lack of oxygen during 

 the metaphase pursue the most peculiar development on re- 



