Originative Factors in Evolution. By J. A. Thomson. 441 



yet cannot explain how he knows ; but there seems good sense 

 in recognizing the latter as a qualitative change. So with the 

 mathematical genius, the musical genius, the artistic genius ; and 

 there is not any reason to believe that man is the only species 

 that produces geniuses. The evidence of their occurrence else- 

 where is in the rapidly growing records of mutations of large 

 amount. There is a mutation-theory, but is there any theory of 

 mutations ? 



On the dark problem of the origin of the distinctively new 

 some beams of light have been shed. («) First, there are facts 

 suggesting that deeply saturating environmental influences may 

 act as variational stimuli on the germ-cells and provoke change. 

 ]\IacDougal injected solutions of sugar and compounds of calcium, 

 potassium, and zinc into the developing ovaries of one of the 

 Evening Primroses, and got out of several hundreds of seeds 

 sixteenindividuals notably atypical, which bred true to the second 

 and third generation. There were not only losses and augmen- 

 tations, there were distinct novelties which maintained their 

 distinctness when crossed with the parental strains. It should be 

 noted that what MacDougal injected was not very much out of 

 the way, and might be paralleled by natural changes in the 

 chemical composition of the sap of the plant. 



Pointing in the same direction are the well-known experiments 

 of Tower, who subjected potato-beetles to unusual conditions of 

 temperature and humidity when the male or female reproductive 

 organs were at a certain stage of development. The results were 

 strangely lacking in uniformity, but some of the offspring showed 

 striking and persistent changes, not only in colour and markings, 

 but also in some details of structure. Tower's work has met with 

 some adverse criticism, but, taken along with similar experiments, 

 it suggests that we must not overlook the possibility of deeply- 

 saturating environmental influences acting as variational stimuli — 

 affecting not the body of the parent, but the germ-cells within. 

 Here should be included Weismann's view that fluctuations in 

 bodily nutrition may prompt the germ-plasm to vary. 



{h) Some of the researches of recent years, such as those of 

 Gates on Evening Primroses ((Enothera) and of Morgan on the 

 Pomace-fly (Drosophila), have focused attention on the chromo- 

 somes. It is a distinct step to know that certain peculiarities of 

 particular mutants are associated with visible alterations in the 

 chromosomes of the fertilized egg-cell. It is very interesting to 

 know that while the fundamental number of chromosomes for the 

 genus (Enothera is fourteen, this has become fifteen in lata and 

 semilata, twenty-one in semigigas, twenty-eight in gigas, and so on. 

 These are the numbers observed in the fertilized egg-shell and in 

 every element throughout the plant. 



In this connexion a reference may be made to what obtains in 



