No. 573] PATTERN DEVELOPMENT 



pletely pigmented, there are certain definite points of 

 the body from which as centers the tendency to develop 

 pigment in the epidermal structures may become less 

 and less. Outward from each of these centers pigment 

 formation spreads to include very definite areas which in 

 wholly pigmented animals overlap slightly at their 

 borders or are at least contiguous. 



2. A reduction in the area covered by any of these 

 primary patches results in a white mark at the line of 

 junction of two contiguous color patches, where no pig- 

 ment is produced. These white marks between the pri- 

 mary patches are spoken of as primary breaks. 



3. Through a study of the breaks in pied individuals 

 of domesticated species of mammals and birds, the 

 boundaries of the primary patches have been determined. 

 These are homologous in the two groups and subject to 

 a certain amount of variation in different types. They 

 are: a median crown patch unpaired, and five paired 

 patches on the opposite sides of the body, which are 

 named from the general areas they cover, the ear, neck, 

 shoulder, side and rump patches. Their limits are more 

 precisely defined under the different species treated. 



4. These patches are physiologically independent of 

 each other and may be differently colored in the same 

 individual. 



5. Pied patterns among many wild species have been 

 brought about through the areal reduction of these pig- 

 ment patches in a definite way so that the white markings 

 resulting as breaks between the reduced patches have 

 become fixed and form a permanent part of the normal 

 pattern. 



6. In several wild species this development of white 

 markings is shown to be even now taking place, but the 

 amount of pigment reduction is still fluctuating so that 

 the white markings vary much in extent with different 

 individuals. 



7. The development of such white markings takes place 

 probably by little and little, so that the departure from 



