214 
R. Ruggles Gates. 
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 Crepidula. In affinis 
the dimensional characters were found to vary from valley to valley. 
A handed 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-handed 
form was also found by Crampton—an entirely new hicoloured 
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. nemoralis. 
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 
J Gates (1917c). 
