NATURAL 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 O. 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, 2 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 Ibid. 



2 Spermatozoa 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. 



