SEX-CHROMOSOMES AND INHERITANCE 187 



parthenogenetic females like themselves (Fig. 86), and 

 this non-sexual process continues indefinitely. If on the 

 contrary, parthenogenetic females are fed abundantly on a 

 rich diet of the green alga Euglena, their eggs develop into 

 individuals which, if early fertilized as explained above, 

 become sexual females, i.e., they lay fertilized eggs, but if 

 not fertilized, produce small eggs that, developing par- 

 thenogenetically, become males. In other words, the same 

 female becomes either a sexual female, or a female that 



Fig. S6.— Diagram showing how a continuous diet of Polytoma (P-P) through twenty- 

 two months yielded only female-producing females, but when the diet was suddenly changed 

 to Chlamydomonas (at C), male-producing females appeared at once. (After Whitney.) 



gives birth to males. Some recent writers, misunderstand- 

 ing these relations, have tried to make it appear that the 

 change here is one that is sex-determining, using this 

 expression to all appearances as it is ordinarily employed 

 in other cases, but in fact using the term in such a way 

 as to obscure the one important fact that the results really 

 show, viz., that an environmental change of a specific kind 

 produces a new kind of female that is either a producer 

 of eggs that become males (after or because two polar 

 bodies are extruded), or becomes a sexual female, should 

 she early meet a male. 



