318 THE ZOOLOGIST. 



on popular imagination. The isolated events to which variation is 

 due are evidently changes in the germinal tissues, probably in the 

 manner in which they divide. It is likely that the occurrence of 

 these variations is wholly irregular, and as to their causation we are 

 absolutely without surmise or even plausible speculation. Distinct 

 types once arisen, no doubt a profusion of the forms called species 

 have been derived from them by simple crossing and subsequent 

 recombination. New species may be now in course of creation by 

 this means, but the limits of the process are obviously narrow. On 

 the other hand, we see no changes in progress around us in the 

 contemporary world which we can imagine likely to culminate in 

 the evolution of forms distinct in the larger sense. By intercrossing 

 Dogs, Jackals, and Wolves, new forms of these types can be made, 

 some of which may be species, but I see no reason to think that 

 from such material a Fox could be bred in indefinite time, or that 

 Dogs could be bred from Foxes. 



Whether Science will hereafter discover that certain groups can 

 by peculiarities in their genetic physiology be declared to have a 

 prerogative quality justifying their recognition as species in the old 

 sense, and that the differences of others are of such a subordinate 

 degree that they may in contrast be termed varieties, further genetic 

 research alone can show. I myself anticipate that such a discovery 

 will be made, but I cannot defend the opinion with positive con- 

 viction. 



Somewhat reluctantly, and rather from a sense of duty, I have 

 devoted most of this Address to the evolutionary aspects of genetic 

 research. We cannot keep these things out of our heads, though 

 sometimes we wish we could. The outcome, as you will have seen, 

 is negative, destroying much that till lately passed for gospel. 

 Destruction may be useful, but it is a low kind of work. We are 

 just about where Boyle was in the seventeenth century. We can 

 dispose of Alchemy, but we cannot make more than a quasi-chernistry. 

 We are awaiting our Priestley and our Mendeleeff . In truth it is not 

 these wider aspects of genetics that are at present our chief concern. 

 They will come in their time. The great advances of science are 

 made like those of evolution, not by imperceptible mass-improvement, 

 but by the sporadic birth of penetrative genius. The journeymen 

 follow after him, widening and clearing up, as we are doing along 

 the track that Mendel found. 



