NatTuRAL DEATH AND FERTILIZATION 739 
began experiments on starfish eggs’ which, however, we were 
not able to complete at that time. In dealing with eggs 
which are as long lived as sea-urchin eggs a great develop- 
ment of bacteria in normal sea-water cannot be prevented, 
since a few of the eggs always die and so serve as an excel- 
lent culture medium for the further development of bacteria. 
It need, therefore, surprise no one that the unfertilized eggs 
of sea-urchins, as I was able to show this year, live in sterile 
sea-water for five days, or possibly longer, while they die 
much earlier in ordinary sea-water (about two days). The 
very fact that the eggs of sea-urchins are found mature in the 
ovary indicates that they are able to live a considerable time 
after maturation and that they differ in this respect from 
the starfish egg. 
It is, however, a fact that in the same sea-water the fer- 
tilized and developing sea-urchin eggs live longer than the 
unfertilized eggs. 
It almost seems as if in certain of the higher animals 
there are eggs which develop only when they are fertilized 
immediately after leaving the ovary. Under the direction of 
Professor C. O. Whitman, Harper has shown that the eggs 
of pigeons are fertilized the moment they leave the ovary. 
The sperm lives in a gelatinous mass upon the surface of the 
ovaries,’ so that provision is made for the necessary contact 
between sperm and egg. This also does away with the diffi- 
culty which many have found in explaining how the sper- 
matozoon finds its way to the egg in animals in which fer- 
tilization occurs within the body. Definite directive forces 
are clearly not necessary, since a portion of the spermatozoa 
must reach the ovary, through their ciliary motion, by way 
of the uterus and Fallopian tubes. Experiments similar to 
1 Tbid. 
2Spermatozoa are in general much longer lived than mature eggs, even though 
great differences exist in this regard in different animals. In the spermatic vesicles 
of the queen bee spermatozoa are believed to remain alive more than a year after 
copulation. 
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