148 ETHEL BROWNE HARVEY. 



same results, and were equally good for observation, the eggs of 

 Echinus being a little larger. 



When the eggs are subjected to lack of oxygen immediately 

 after fertilization (Fig. i), the sperm aster forms and the two 

 pronuclei approach just as under normal conditions, there 

 being still sufficient oxygen for normal development. After 

 about twenty minutes, however, the process is arrested owing to 

 lack of oxygen. In some cases this takes place when the two 

 pronuclei are still a little distance apart (Fig. 2). If kept in 

 absence of oxygen, the sperm aster gradually fades out and 

 the cell appears just as it did on fertilization (Fig. 3). This 

 usually occurs in 40 to 60 minutes after admission of hydrogen 

 to the chamber (room temperature i6-i8). In most cases 

 the female pronucleus is still visible even after two or three 

 hours in hydrogen, but in some cells it cannot be discerned. 

 In most of my experiments at this stage, the cells became irregular 

 in outline after about forty minutes in hydrogen, sometimes 

 earlier, and much crinkled, showing decidedly light and dark 

 areas of protoplasm, and they remained in this condition, 

 gradually increasing in intensity for two or three hours (Figs. 4 

 and 5). I am inclined to think that this is due, however, to 

 other conditions than lack of oxygen since in two experiments 

 most of the eggs remained uncrinkled and quite normal in 

 appearance, and sometimes eggs under apparently normal con- 

 ditions show the same peculiarities. They are somewhat similar 

 to eggs kept in hypertonic sea water, although it cannot be due 

 here to withdrawal of water since the same eggs in the same 

 chamber later became smooth again. 



When oxygen is admitted, the sperm aster reappears, in the 

 same position where it disappeared, in the course of half an 

 hour in the clear uncrenulated eggs, and development goes on 

 in quite a normal fashion though all the stages are of course 

 delayed. In the crenulated eggs, the dense protoplasm obscures 

 the nuclear phenomena, and usually the mitotic figure is in the 

 early metaphase before asters or nuclei are discernible (Fig. 6). 

 Even though much crinkled and irregular, these eggs straighten 

 out, become regular in outline and normal in appearance. The 

 only abnormality observed in the development of the eggs 



