Natura DEATH AND FERTILIZATION 735 
eggs live longer. We begin with the experiment which is 
technically most simple. The eggs streaming from the 
ovary are divided into two portions. One portion of eggs 
is carefully distributed without mechanical agitation, by 
carefully tipping the vessel, in a thin layer over the bottom 
of the vessel. The vessel must be low and the layer of sea- 
water covering the eggs not too deep, so that the diffusion 
of oxygen to the eggs can occur withease. A second portion 
is introduced with just as great care into a small-calibered 
glass tube sealed at one end. This glass tube is half filled 
with eggs so that one is certain that the lower layers of the 
eggs in the pipette receive little or no oxygen. It is self- 
evident that the eggs must be introduced into the tube 
immediately after being laid. When, after twenty-four 
hours, the eggs which are distributed over the bottom of the 
glass dish and which receive a large amount of oxygen are 
compared with those at the bottom of the glass tube, a 
striking difference is found between them. The eggs richly 
supplied with oxygen contain a much larger percentage of 
mature dead and black eggs than those kept in the lack of 
oxygen. In the latter the living immature eggs are in the 
majority, and a part of these maturate when spread out in a 
thin layer over the bottom of a vessel. These experiments 
are also well adapted to show that the rapid death of the 
mature unfertilized sea-urchin eggs is determined through 
internal conditions and not by the bacteria contained in the 
sea-water. I will cite an example. 
One portion of a lot of eggs was spread out in a thin 
layer over the bottom of a dish; another was heaped ina 
mass in the same dish. The sea-water was the same in both 
cases. The first portion of eggs matured in a few hours and 
were, in less than twelve hours, opaque and dead, while the 
water was still absolutely clear and without odor of putrefac- 
tion. After twenty-four hours the water became putrid and 
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