Mutations in Animals. 75 



as a monstrosity." Featherless birds are not unknown, or only 

 certain pterylae may be affected, as in the bareneck fowls (Davenport, 

 1914), a condition which is dominant in crosses. A well known 

 case cited by Stebbing is that of Dorippe dorsipes with four legs, 

 and four more small ones on its back. It is therefore clear that 

 even mutationat monstrosities have played their part in the 

 production of species, and it is quite certain that if some family and 

 ordinal characters could have been seen at their first appearance 

 they would have been considered monstrosities. 



Dwarfs and giants are as common in animal species as among 

 plants. A dwarf-bearing strain of guinea pigs is described by Miss 

 Sollas (1914). It produced in all 192 normals to 64 dwarfs, the latter 

 evidently behaving as a simple Mendelian recessive. The study of 

 inheritance of melanism in British Lepidoptera has in recent years 

 attained considerable proportions. These results can only be 

 touched upon here, but they show that the melanic variety usually 

 behaves as a Mendelian dominant, sometimes a recessive, and in 

 certain cases gives blending inheritance. A number of cases are 

 discussed by Bateson (1913, p. 135 ff.) 



Sumner (1917) has obtained mutations in the Californian deer- 

 mouse, Peromyscus tnaniculatus, both in the wild state and in 

 captivity. A " yellow " mutation of P.m. gambeli was trapped at 

 LaJolla, California in 1914. The normals have a dark gray pellage 

 and black eyes. In cages a total of 14 normal to 7 yellow appeared, 

 in broods which were traced back to a single pair of grandparents. 

 There were no other yellows among over 400 gambeli bred. Hence 

 the appearance of the yellow was due to a recessive mutation 

 factor carried in the two grandparents. Castle has reported 

 similar "yellow sports" in wild species of Mierotus. 



