4 THE ROYAL SOCIETY OF CANADA 



various steps and "with good, unsought experiments by the way," 

 has led to the remarkable achievement of what has been termed 

 artificial parthenogenesis. It has been found that certain chemical 

 modifications of the environment suffice to stimulate the ovum to 

 proceed on its pathway of development quite independent of any union- 

 with the male element, and thereby it has been made clear that two 

 distinct phenomena are included in the process of fertilization, one 

 being of the nature of a stimulus, which, as it were, disturbs the equili- 

 brium of the ovum and releases the potentialities for development. 

 It may be added that quite recently the application of methods based 

 on those employed in the investigation of immunology has led Lillie 

 to results which promise a more definite understanding of the modus 

 operandi of this factor in fertilization. 



But while the energies of many zoologists were devoted to f/Dllow- 

 ing out these newer lines of research, others continued to elaborate the 

 older lines and, turning from studies of cell-lineage, they began to 

 focus their attention on the germ-cells and especially upon the struct- 

 ural changes in these preceding and accompanying fertilization. 

 Improvements in the microscope and in microscopic technique had 

 made such studies possible, and in 1875 Oscar Hertwig demonstrated 

 that what then seemed to be the essential phenomenon of fertilization 

 was the union of the nuclei of the two conjugating germ-cells, and 

 followed up this discovery some twelve years later by showing that the 

 changes occurring in both germ-cells prior to fertilization were identi- 

 cal, so that the nuclear fusion was the union of two quantitatively 

 like structures. The natural conclusion from this was that the nuclei 

 were the structures chiefly concerned in the phenomenon of heredity, 

 a conclusion fortified by observations which revealed in detail the 

 mechanism of the nuclear union with its chromosome reduction and 

 pairing, and eventually located in the chromosomes of the nuclei 

 the material bearers of heredity and the determiners of sex. 



Although the older method of direct observation has not been 

 neglected by zoologists the great characteristic of present-day zoology 

 is the application of the experimental method. Darwin in discussing 

 the origin of species took heredity and variation for granted and did 

 not at first speculate as to how they were accomplished. But even 

 while zoologists were still immersed in phylogenetic studies the question 

 as to the mechanism of inheritance would obtrude itself, and in the 

 eighties and nineties the speculations of Weismann precipitated a 

 vigorous discussion as to the inheritance or non-inheritance of acquired 

 characters, a discussion that dragged its weary length along for many 

 years. But it was just about the time that it became prominent that 

 experimental methods began to be applied to morphological problems. 



