18 



The Mechanistic Conception of Life 



How is sex determination accomplished ? Let us take 

 the case which according to Wilson is true for many insects 

 and according to Guyer for human beings, namely, that there 

 are two kinds of spermatozoa and one kind of eggs. According 

 to Wilson all unfertilized eggs contain in this case one so-called 



Figs. 11-16 (after E. B. Wilson). — Diagrammatic presentation of sex deter- 

 mination in an insect (Protenor). a a are the nuclei of im^fertUized eggs. Each 

 contains one sex cliromosome marked X; the other six dark spots are the chromo- 

 somes which are supposed to transmit hiereditary characters not connected with 

 sex. b and c represent the two different types of sperm; b containing a sex 

 chromosome X, c being without such a chromosome. 



d represents the constitution of the egg nucleus after it is fertilized by a 

 spermatozoon of the type b containing a sex chromosome. This egg now has two 

 sex chromosomes and therefore wiU give rise to a female, e represents a fertilized 

 egg after a spermatozoon of the type c (without a sex chromosome) has entered it. 

 This egg contains after fertilization only one sex chromosome X and hence will 

 give rise to a male. 



sex chromosome, the X-chromosome. There are two kinds 

 of spermatozoa, one with and one without an X-chromosome. 

 Given a sufficiently large number of eggs and of spermatozoa, 

 one-half of the eggs will be fertilized by spermatozoa with 

 and one-half by spermatozoa without an X-chromosome. 

 Hence one-half of the eggs will contain after fertilization two 

 X-chromosomes each and one-half only one X-chromosome 



