A METHOD TO TEST THE HYPOTHESIS OF 

 SELECTIVE FERTILIZATION. 



T. H. MORGAN, F. PAYNE and ETHEL N. BROWNE . 



The hypothesis of selective fertilization has played an impor- 

 tant role in several recent theories of sex determination and to 

 some extent also in modern Mendelian speculations. It has been 

 assumed for example that there are two classes of spermatozoa 

 and two classes of eggs — male and female eggs and male and 

 female sperm — and that fertilization is reciprocal in the sense 

 that a male sperm can only fertilize a female egg and that a female 

 sperm can only fertilize a male egg. On the other hand the 

 more commonly accepted view is that any sperm can fertilize any 



Until this question is settled by direct observation or by experi- 

 ment these two alternatives will continue to make uncertain our 

 interpretations. 



To put together one sperm and one egg would seem to be the 

 simplest way to test the question. The operation may not in 

 itself present insuperable difficulties but the chance of the sper- 

 matozoon reaching the surface of the egg is so small as to make 

 the attempt rather hopeless ; for there is no evidence to show 

 that the spermatozoon is attracted towards the egg. The work 

 of Buller, in particular, shows that accident alone determines the 

 •contact between the spermatozoa and the membranes, or the jelly, 

 of the egg. 



By means of the following simple method we have found it 

 possible to study the problem of selective fertilization. We feel 

 that while the number of cases here recorded is too small to 

 settle so important a question, its application on a larger scale 

 and on other animals should furnish conclusive evidence for or 

 against selective fertilization. 



We wish therefore at present to lay more emphasis on the 

 possibilities of the method than on the certainty of demonstra- 

 tion from the number of recorded cases, and hope that others 



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