FERTILIZATION 65 



the marvelous array of characteristics that make up the 

 sum total of what is obviously inherited in man, the 

 wonder grows that so small a bridge can stand such an 

 enormous trafnc. A sharp-eyed patrol of this bridge that 

 is the strategic focus of heredity is proving to be one of 

 the most effective points of attack in the entire campaign 

 of genetics." 



8. Artificial Fertilization. The process described in 

 this chapter varies considerably in different species of 

 animals and plants, but what has been said will serve to 

 give you an idea of what occurs in the great majority of 

 eggs and sperms that develop into adult plants or animals. 

 Usually an egg dies and disintegrates if it is not fertilized 

 by a sperm nucleus. However, a most wonderful discovery 

 was made only a few years ago. Some eggs of sea- 

 urchins were experimented with. Now the eggs of sea- 

 urchins, so far as we know, never develop without being 

 fertilized. But a scientist took such eggs directly from 

 the ovary, where they could not have been exposed to 

 sperms, and by putting them in water of a different density 

 from that of ordinary sea water and then returning them 

 to the sea water, he succeeded in haA ing them begin to 

 develop, instead of die and decompose as they would 

 naturally do without fertilization. In other words, by 

 outside chemical stimulation, eggs were "artificially 

 fertilized," so that they began to develop without uniting 

 with sperms. This work has been repeated many times 

 since, and we find that the same thing is possible with 

 many different kinds of eggs; of worms, mollusks, and 

 even of vertebrates. It is also found that numbers of 

 other chemical substances and even other kinds of stimuli 

 may so arouse these eggs as to start development. All 

 of this suggests that the work of the sperm is to act as 

 a stimulant to the sluggish egg, and cause it to become 

 active in development, when it could not do so unaided. 



