200 SPECIES AND VARIETIES. 



cur in nature, but assuredly it is not the normal process. There 

 is no reason for systematists to change their attitude in regard 

 to the species-concept. If they have been estranged from Genet- 

 ics by the fact, that they were in possession of evidence which 

 showed species to be unchanged for long periods of time, it is to 

 be hoped that their interest in Genetics can be revived and a 

 better cooperation made possible. As to the stability of species, 

 we have now to concede to the systematists the correctness of 

 their view. Is the attitude of these observers toward species and 

 varieties and their nature warranted by the facts, and is their 

 method of applying names still adequate? We are convinced it 

 is. Varieties cannot be truly said to be descended from species 

 in the way in which species descend from each other, in so far 

 as this implies that at a certain moment a variety begins life as 

 such, by diverging from the main body. A variety has no nec- 

 essary continuity through any number of generations and as 

 the individuals which can be brought together under one varie- 

 tal name, have their origin in chance combinations of gametes 

 deficient in the same gene, or of gametes which bring into the 

 zygote two genes, which only in combination have a definite 

 action on the development, varieties usually differ from spe- 

 cies to which they belong, in the effect of one gene less or one 

 gene more. We must remember, that such variations between 

 the members of a species as are due to presence and absence of 

 genes having only a very slight influence on the development 

 will commonly be classed as falling within the normal fluctu- 

 ating variability of the species. A systematical description of a 

 iauna or flora cannot be expected to be other than partially 

 complete. 



Only striking varieties, varieties in other words, which owe 

 their difference from the type to a difference through pres- 

 ence or absence of a gene, which has a striking definite effect 

 on the development, will receive a name. A difference in pres- 

 ence or presence of one such a gene will translate itself in a 

 difference in one character mostly. Of course there are several 

 instances in which a gene has a definite influence on more than 



