EXPERIMENTAL ZOOLOGY I97 



the discovery that in many of the lower forms the sex is de- 

 termined either in the egg or not later than the time of fertil- 

 ization. While waiting for a more convenient terminology, 

 we are speaking of "male-producing spermatozoa" and 

 "female-producing spermatozoa," of "male eggs" and "female 

 eggs," meaning by these terms that the protoplasm of a given 

 germ cell is destined to produce a particular sex, irrespective 

 of the influences which are brought to bear in the course of 

 its subsequent development. It is interesting to note that the 

 most important discovery of all in this connection, that of the 

 "accessory chromosome" (a portion of the nucleus which 

 appears to be the sex determinant), has been accomplished by 

 observational rather than by experimental studies, since this 

 illustrates how the clue which experimentation must follow 

 is often given by purely observational work. 



Sex and its determination is one of the most interest- 

 ing and elusive questions in experimental zoology today; and 

 we have made real progress toward its solution by the accumu- 

 lation of evidence all pointing to the germ cell and not the 

 larval stages as the place where the sex of the individual is 

 established once for all. Although this does not bring us 

 very near to the control of sex production in the offspring, 

 it is a step in the right direction if we convince ourselves 

 that by no amount of changed conditions to which we may 

 subject the developing organism can we alter the maleness 

 or femaleness which has been established either before or at 

 the time of fertilization. At least we know the point of 

 attack, even if the problem of how to control the sex now 

 seems all the more difficult. We are, however, pressing so 

 closely upon the question, that sooner than one thinks we may 

 grasp not alone the factors which normally determine the sex, 

 but also the method by which these factors may be modified, 

 and the sex thereby controlled. 



Before leaving this topic, it may interest you to know 

 that very suggestive results have been obtained which tend 



