LIFE AND EXPERIMENT 



however, where eggs removed from the animal yield one 

 hundred per cent, development. Here it is necessary to 

 know that the quality of development parallels that of 

 eggs normally laid under natural conditions. By compar- 

 ing the development of eggs in their normal environment, 

 of those naturally shed in the laboratory and of those 

 removed from the animal, one can decide concerning the 

 normality of the last named. 



In rare cases, where always some immature eggs incap- 

 able of development are present, one may never obtain 

 large numbers of developing eggs, yet those that develop 

 are normal. Similarly, at the end of a breeding season 

 animals frequently give, among those eggs that develop 

 perfectly, some that fail to develop because they have 

 passed the time of optimum condition for fertilization. 

 For such eggs we can not use the criterion of the percentage 

 of development to detect their condition; they can only 

 then be considered to be wholly normal, if their develop- 

 ment is normal at every stage. 



Now the necessity of following the egg throughout its 

 complete development can be obviated. I was able to 

 establish definite criteria and simple physiological indicia of 

 the optimum condition of eggs. These signs tell us within 

 the first minutes after fertilization whether the eggs are in 

 optimum condition and even indicate whether the eggs 

 will be normal throughout their development. The signs 

 inhere in the reactions following the mixing of eggs and 

 spermatozoa and are in a measure as specific as the given 

 gametes themselves. For any given egg, they appear 

 differently when the egg is abnormal. For the eggs of a 

 common sea-urchin, Arhacia, I found that their optimum 

 condition, whether they are normally shed, induced to be 

 shed by artificial means, or removed from the ovaries, can 

 be determined within three minutes after insemination by 

 the rate and quality of membrane-separation; by the 



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