Mutations in Animals. 73 



arisen, evidently by mutations, and others have extended or in 

 some cases retracted their area of distribution. The writer states 

 that "mutation has been demonstrated in numerous instances, and 

 in many species belonging to several islands." It is concluded that 

 the morphological differences which appear are due to "spontaneous 

 congenital causes that remain unknown in themselves" but whose 

 effects are produced independently of environment, isolation of the 

 forms in different valleys merely preventing an intermingling of 

 populations. 



To mention a few cases of variation in the Tahitian forms, 

 Partula otaheitana rubescens, an exclusively sinistral sub-species, 

 occurs in red and yellow varieties, the former being apparently a 

 a simple Mendelian dominant. P. o. affinis has a dextral coil, but 

 sporadic sinistral mutants occur. Similar reversals of symmetry 

 are also known in other Gasteropods, such as Crepidnla. In affinis 

 the dimensional characters were found to vary from valley to valley. 

 A banded form found by Garrett in a restricted locality now occurs 

 in 20 separated regions of Tahiti, apparently as the result of 

 independent mutations in the local populations. A red-banded 

 form was also found by Crampton an entirely new bicoloured 

 pattern. Giants also appear in the sub-species affinis and sinistrorsa, 

 and dwarfs in certain colonies of rubescens and other large snails. 

 With regard to inheritance of banding in land-snails, Lang (1912, 

 etc.) has interpreted it in Mendelian terms from breeding experiments 

 with the European Helix hortensis and H. nenioralis. 



In the plumage of birds, dichromatism or the existence of two 

 interbreeding colour varieties, is a characteristic of many species, 

 and the condition has apparently arisen through a mutation. As 

 a typical case, the red and grey phases of the North American owl, 

 Otus asio, have been discussed elsewhere, 1 the red being apparently 

 a simple Mendelian dominant to the grey phase. 



A remarkable case of an inherited variation in goats, which 

 involves the nervous system, is recorded (Hooper, 1916) from 

 Tennessee. In the central and eastern part of the State there is 

 a breed in which, when suddenly frightened, the hind legs become 

 stiff and the animal jumps along. If greatly frightened the front 

 legs also become stiff and the animal falls to the ground rigid. 

 These stiff-legged goats are preferred because they do not jump 

 fences, but it is obvious that in nature such a variation in any 

 mammal with preying enemies would be eliminated by natural 

 Gates (1917c). 



