A Kew Theory of Heredity. 83 



ova by direct inheritance, the characteristic will be es- 

 tablished as an hereditary race characteristic, and will 

 be perpetuated and transmitted, by the selected individu- 

 als and their descendants, without gemmules. 



According to this view, the origin of a new variation is 

 neither purely fortuitous nor due to the direct and definite 

 modifying influence of changed conditions. A change 

 in the environment of a cell causes it to throw off gem- 

 mules, and thus to transmit to descendants a tendency 

 to vary in the part which is affected by the change. 



The occurrence of a variation is due to the direct 

 action of external conditions, but its precise character is 

 not. My view of the cause of variation is thus seen to be 

 midway between that accepted by Darwin and that advo- 

 cated by Semper and other Lamarkians. 



Many naturalists have given reasons for believing that 

 the transmutation of species is not always gradual, but 

 that a form which has long persisted without change may 

 suddenly vary greatly, and thus give rise to a strongly- 

 marked race of descendants. Mivart has discussed this 

 subject at considerable length, and he quotes Professor 

 Huxley's opinion that *^we greatly suspect that Nature 

 does make considerable jumps in the way of variation 

 now and then, and that these saltations give rise to some 

 of the gaps which appear to exist in the series of known 

 forms;" and Dall has proposed the term saltatory evolu- 

 tion for abrupt change of this kind. According to the 

 theory here advanced, variation must tend to accumulate 

 or culminate, and one variation must cause others;, for 

 when any particular cell changes, the harmonious ad just- 

 ment between it and adjacent or related cells will be dis- 

 turbed, and all the cells which are tbus affected will tend 

 to throw off gemmules, and thus to induce variability in 

 the same cells of succeeding generations. Then, too, a 



