112 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



B. Partial Albinism. 



1. Manner of occurrence. Partial albinism is a phenomenon of not 

 infrequent occurrence among mammals and birds, and other organisms as 

 well. In many species the unpigmeuted areas form part of a definite color 

 pattern and may be in the form of stripes or spots variously disposed. 

 Such markings, however, appear to come under a category different from 

 that of the white areas occurring abnormally in animals that naturally are 

 pigmented over all parts of the body. In the case of such animals, spots 

 or unpigmented areas, when they occur, tend to ap^^ear at certain definite 

 places, and the increase of the white areas takes place in such a way 

 as to give the impression that the pigment is shrinking away toward 



Figure 3. 



Figure 4. 



certain centres more or less definitely situated. The writer's atten- 

 tion was first called to this matter by Professor Castle in the case 

 of guinea pigs, where these centres are especially conspicuous. From 

 a study of a number of spotted mammals the writer has made out 

 in several of them the presence of ten such centres (see Figures 

 3-G). These are bilaterally arranged five on either side, as follows: 

 (1) A genal centre for the pigment patch which embraces the eye, 

 ear, and side of the face ; (2) a nuchal centre for the neck patch ; 

 (3) a scapular centre for the patch which covers the shoulder and 

 fore leg ; (4) a pleural centre for the side patch ; (5) a sacral centre 

 for the large patch which includes the tail, hind limbs, and sacral region. 

 Figure 3 shows in a diagrammatic way the location of these centres 

 in the house mouse. On account of the shortness of the neck in the 



