DARfelSHlRE : l''ROFESSOR LANg's BREEDING EXPERIMENTS. 109 



of the supposed DD and DR parents. For the o parent of experiment 

 49, in which its behaviour is consistent with the theory that it was a 

 dominant, and the o parent of experiment 55 which Lang suggests 

 was a hybrid, both appeared in the brood produced in experiment 28 

 in which both o and 5 appear, and which appears under the heading 

 of " experiments in which it is certain that the mother was o, but in 

 which it is not quite certain that the father bore this character."^ 

 There is a ratlier interesting difference between the ancestry of the 

 snails used in experiment 49 and those used in experiment 55, but it 

 Hes not in a difference for which there is only a priori evidence in the 

 ancestry of the o, but in an actual difference in that of the 5 ; for, 

 while in experiment 49, in which the o appeared to be dominant, the 

 5 was of parentage 9 5 x c^ ? 5 ; in experiment 55 where the o appeared 

 to be a hybrid the parentage of the 5 was 9 o x $1 o ; and it looks as 

 if the less pure-bred a five-banded snail were, the more power it had 

 of transmitting its five-bandedness; a state of affairs which is com- 

 parable with what seems to obtain in the case of my mice, namely, 

 that the more pure-bred an albino is, the less power it has of trans- 

 mitting its whiteness to its offspring when crossed with a Japanese 

 waltzing mouse. But that this difference in the parentage of the five- 

 banded parent is not the only factor which may account for the 

 production of o and 5 from o x 5 is evident from the fact that in 

 experiment 59 where this occurs the 5 is of parentage ? 5 x $} "^ and 

 not 0x0. The only common factor which I can trace in the 

 characters of 5's which when mated with o's have produced o and 5, 

 is that there is a considerable tendency to the fusion of bands in the 

 banded parents in experiments 55 and 59. 



Helix nemoralis and H. hortensis can be distinguished from one 

 another by the fact that the former usually has a dark, and the latter 

 a pale, lip ; but dark-lipped H. hortensis are not rare, and pale-lipped 

 H. nemoralis are occasionally found. An experienced conchologist 

 can separate the two species at a glance by the general look and size of 

 the shell. But if his verdict is questioned, an examination of the dart 

 decides the matter ; the darts of the two species are quite discontinu- 

 ously distinct. Conchologists believe that the sum of the distinguishing 

 characters justifies them in pronouncing H. hortensis andZ^ nemoralis 

 distinct species ; and their conviction is not shaken by the discovery 

 that these two snails are sometimes mutually fertile. One looks 

 forward with the greatest interest to Professor Lang's description of 

 the dart of the H. nemoralis x H. hortensis hybrid. Many of the 

 facts he has already recorded are of great interest. The altitude of 

 the shell in three of the hybrids was greater than that of either parent 



I p. 476. 



