242 SECRETS OF ANIMAL LIFE 



potentially before, during, or after fertilization. 

 In short, there is nothing hard and fast about 

 the origin or nature of mutations: their common 

 features are their brusque appearance, their dis- 

 continuity with the parent stock, and their capa- 

 bility of being transmitted intact to a certain 

 proportion of the offspring. This brings us to notice 

 the recent masterly work of Dr. Ruggles Gates, who 

 has been for many years a persistent investigator 

 of the mutations of (Enothera. In his Mutation 

 Factor in Evolution (Macmillan, 1915) he expounds 

 the notable advance which his researches have 

 secured. He has been able to show in circumstan- 

 tial detail that the peculiarities marking the various 

 mutants are correlated with observable alterations 

 in the organization of the fertilized egg-cell, especi- 

 ally as regards the nuclear rodlets or chromosomes 

 of which each kind of organism has a definite num- 

 ber. The fundamental number of chromosomes for 

 the genus CEnothera is 14; this has become 15 in lata 

 and semilata, 21 in semigigas, 28 in gigas, and so on. 

 This change is observable in the fertilized egg-cell 

 and is echoed throughout the whole plant. In this 

 connection a reference may be permitted to what 

 obtains in man. Competent observers have stated 

 that the cells of the male negro have 22 chromo- 

 somes, and it is probable that the negress has, at 

 least in some cases, 24. Now in the case of the white 

 man and woman the enumerations of chromosomes 

 by very careful observers point to the numbers 

 47 and 48 respectively. It seems to be very difficult 



