December 9, 1904.] 



SCIENCE. 



781 



polemics become superfluous. It was, 

 therefore, a decided progress when de 

 Vries was able to show that the hereditary 

 changes of forms, so-called 'mutations,' 

 can be directly observed, at least in certain 

 groups of organisms, and secondly, that 

 these changes take place in harmony with 

 the idea that for definite hereditary char- 

 acteristics definite determinants, possibly 

 in the form of chemical compounds, must 

 be present in the sexual cells. It seems to 

 me that the work of Mendel and de Vries 

 and their successors marks the beginning 

 of a real theory of heredity and evolution. 

 If it is at all possible to produce new 

 species artitieially I think that the dis- 

 coveries of Mendel and de Vries must be 

 the starting point. 



It is at present entirely unknown how 

 it happens that in living organisms, as a 

 rule, larger quantities of sexual cells be- 

 gin 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 more secondary 

 feature of this phenomenon, namely, that 

 the sexual cells in the salmon apparently 

 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 problem which belongs 

 to this group of phenomena, namely how 

 it happens that in many species one indi- 

 vidual forms sperm, the other eggs. It 

 lias 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 foi-ms, as a rule 

 at least, only males originate from the un- 

 fertilized eggs; from the fertilized eggs 

 only females. It i.s, 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 deter- 

 mined in the unfertilized egg, or at least 

 immediately after fertilization. I consider 

 it possible that in regard to the determina- 

 tion 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 organisms appears, 

 perhaps, most striking -when we compare 

 the many automatic devices by which the 

 preservation of individuals and species is 

 guaranteed. Where separate sexes exist 

 we find automatic arrangements by which 

 the sexual cells of the two sexes are brought 

 together. Wherever the development of the 

 eggs and larvae occurs outside of the body 

 of the mother or the nest we often find au- 

 tomatic 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 question 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 performs, 

 without foresight of the ends, those acts 

 by which the preservation of the individual 

 or the species is secured. The term 'will' 

 is reserved for those cases where these proc- 



