226 Expcrimen ta I Zoology 



Even if the new form is adapted to the same locality as the 

 parent species, it may ripen its germ-cells at a different time, and 

 this will again increase its chance of isolation from the parent 

 species. 



If the new form is only a variety in de Vries's sense, it will get 

 an opportunity of surviving in another way. Suppose it does 

 back-cross in the first generation, it will reappear in every succeed- 

 ing generation, so that it may go on increasing in numbers every 

 year. If it should be a form with better chances of survival 

 than the parent, it may subsequently become the more common 

 type. 



It has been shown, especially in some animals, that the new 

 mutation may dominate in crosses with the parent form. Con- 

 sequently, in the next generation it may appear in many indi- 

 viduals, and the number of new individuals will increase in every 

 generation. Should the new character follow Mendel's law, 

 some of the hybrids will be pure, others mixed ; but in either case 

 the opportunity of surviving is given, and if the dominating type 

 is at all capable of existing, it will always remain in existence, 

 and, under certain conditions, as when, for instance, it is better 

 suited than the parent form to another locality, it may establish 

 itself there. 



The important experimental results of Standfuss bear directly 

 on the problem of the crossing of new mutations with the 

 parent species. He describes a number of cases that he has 

 himself observed, and records a number of aberrations recorded 

 by other entomologists, in which a new type was crossed with 

 the parent stock. A few cases are also given in which two 

 aberrations were inbred. In both groups the offspring were 

 either like the -parent species or like the aberration, and no inter- 

 mediate forms were produced. These results were obtained in 

 the first generation of hybrids. In a few cases a new genera- 

 tion was also reared and the same phenomenon of splitting was 

 observed. These results show that a new type that appears may, 

 even if crossed with the parent species, reproduce itself in its pure 

 form without blending. The process continuing in succeeding 



