18 BIOLOGY 



It is at present entirely unknown how it happens that in living 

 organisms, as a rule, larger quantities of sexual cells begin to form 

 at a definite period in their existence. Miescher attempted to solve 

 this problem in his researches on the salmon. But it seems that 

 Miescher laid too much emphasis upon a mere secondary feature of 

 this phenomenon, namely, that the sexual cells in the salmon ap- 

 parently develop at the expense of the muscular substance of the 

 animal. According to our present knowledge of the chemical dynamics 

 of the animal body it seems rather immaterial whether the proteins 

 and other constituents of the sexual cell come from the body of the 

 animal or from the food taken up. The causes which determine the 

 formation of large masses of sexual cells in an organism at a certain 

 period of its existence are entirely unknown. 



A little more progress has been made in regard to another prob- 

 lem which belongs to this group of phenomena, namely, how it hap- 

 pens that in many species one individual forms sperm, the other 

 eggs. It has been known for more than a century that it is possible 

 to produce at desire either females exclusively, or both sexes, in 

 plant lice. In bees and related forms, as a rule at least, only males 

 originate from the unfertilized eggs; from the fertilized eggs only 

 females. It is, moreover, known that in higher vertebrates those 

 twins which originate from one egg have the same sex, while the sex 

 of twins originating from different eggs may be different. All facts 

 which are thus far known in regard to the determination of sex 

 seem to indicate that the sex of the embryo is already determined 

 in the unfertilized egg, or at least immediately after fertilization. 

 I consider it possible that in regard to the determination of sex, 

 just as in the case of artificial parthenogenesis, a general variable 

 will be found by which we can determine whether an egg cell will 

 assume male or female character. 



V. Instinct and Consciousness 



The difference between our artificial machines and the living organ- 

 isms appears, perhaps, most striking when we compare the many au- 

 tomatic devices by which the preservation of individuals and species 

 is guaranteed. Where separate sexes exist we find automatic arrange- 

 ments by which the sexual cells of the two sexes are brought together. 

 Wherever the development of the eggs and larvse occurs outside of the 

 body of the mother or the nest we often find automatic mechanisms 

 whereby the eggs are deposited in such places as contain food on 

 which the young larva can exist and grow. We have to raise the ques- 

 tion how far has the analysis of these automatic mechanisms been 

 pushed. Metaphysics has supplied us with the terms " instinct " and 

 " will " for these phenomena. We speak of instinct wherever an animal 



