152 ETHEL BROWNE HARVEY. 



resulting in a continuation of mitotic division, while the proto- 

 plasmic life was arrested, no streaming of protoplasm taking 

 place and no cell divisions. Such a distinction can certainly 

 not be made in the case of the sea urchin egg, for practically all 

 manifestations of life are inhibited by lack of oxygen, both 

 nuclear and protoplasmic. 



The fading out of the astral fibers and disappearance of the 

 mitotic figure which resulted from exposure to lack of oxygen, 

 are of interest in comparison with the early experiments of the 

 Hertwigs ('87 and '90) with chloral hydrate, quinine and cold, 

 and those of Wilson ( ! oi) on ether. Perhaps the disappearance 

 is even more complete in the case of absence of oxygen, for all 

 traces of fibers, astral rays and astrospheres may be lost. 



As indicated above, the lack of oxygen had practically no 

 effect on subsequent development during any of the earlier 

 stages of mitotic division. The astral rays and spindles come 

 back in the same place and condition when oxygen is readmitted 

 as they were before oxygen was taken away. It is only when 

 oxygen is taken away during the full metaphase or a little after 

 that the reappearing mitotic figure is different and the subsequent 

 cleavages are aberrant, although even here normal larvae are 

 produced. This is contradictory to the results of E. P. Lyon 

 ('02), who found that sea urchin eggs were most susceptible to 

 lack of oxygen and to cold 10-15 minutes after fertilization. 

 Although in my experiments, eggs were not in total absence of 

 oxygen till 15-20 minutes after fertilization, they were at a 

 lower temperature (i.e., i6-i8 as opposed to 20 of Lyon) 

 so that most likely his susceptible period was covered. The 

 period that was most susceptible in my experiments was the 

 metaphase and slightly later, a period which Lyon ('02, '04) 

 found most resistant to lack of oxygen and cold but most sus- 

 ceptible to heat and most productive of COa. However, the 

 criterion of susceptibility was different in his experiments and 

 mine, his being the total number of survivors and mine being the 

 microscopic appearance of individual eggs. The fate of the 

 larvae was quite precarious in my experiments, some lots of 

 eggs going well and others under apparently identical conditions 

 not surviving the following morning. When conditions are 



