116 PROCEEDINGS OF THE AMERICAN ACADEMY. 



soma, though the cross with the albino served to call forth the produc- 

 tion of a greater amount of coloring matter. The precise mechanism by 

 which this result is obtained is not clear ; it is uncertain whether there is 

 simply an increase of a pigment-producing ferment, as Cuenot's explana- 

 tion would imply, whether the cross with an albino serves to upset an 

 unstable condition, or whether some other unknown influence brings about 

 the result. At all events, the facts thus far collected seem to indicate 

 that the albinos used in these cases transmit a character which makes for 

 total pigmentation, and this asserts itself in the first hybrid generation as 

 a character dominant over partial pigmentation. 



What is probably an analogous result is recorded by Tschermak (: 02) 

 in the case of peas (Pisum). The usual type of P. arvense is character- 

 ized by the presence of red pigment spots at the axils of the leaves. A 

 Swedish variety was obtained which lacked this spot and bred true to 

 the peculiarity. But hybrids obtained by crossing this pea with an 

 albino stock were found to exhibit the red axillary spot. This phe- 

 nomenon may also be looked upon as a case in which a character 

 emerges from latency under the influence of cross breeding, the charac- 

 ter missing in one parent having been transmitted through the albino 

 parent to the offspring, in which it becomes active. 



It is clear, then, that a white animal with black eyes is not an albino, 

 but simply a partial albino, and care must be taken to recognize this fact 

 in studying the heredity of albinism. 



In practically all domesticated animals partial albinism occurs to a 

 greater or less extent, and it is quite possible that the conditions incident 

 to domestication favor its appearance, or at least its propagation. Among 

 animals living under natural conditions also partial albinism is not infre- 

 quent, often appearing among small mammals in the form of a white tip 

 to the tail. Thus Miller ('93) records having found white-tipped tails 

 repeatedly in the case of the two eastern species of white-footed mouse 

 {Peromyscus), and occasionally in 3Ius musculus, likewise in the vole 

 {Mlcrotus pennsylvanicus) , and in the common Blarina (Blartna brevi- 

 cavda). In the common jumping mouse {Zapns Imdsonius) Miller has 

 twice found specimens, otherwise perfectly typical, having a white tip to 

 the tail, 8 ram. in extent. He points out that in the nearly related 

 woodland jumping mouse (Napaeozapics) this character has become 

 a distinctive mark. It would thus appear that the character is capable 

 of inheritance and fixation. What causes bring about such a restriction 

 of pigment seems as yet past finding out, but if the ideas already ad- 

 vanced are correct concerning the development of the pigment from 



