238 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



corium, and that of the latter on the epidermis is particularly 

 complete. Other writers had, however, made a beginning. 

 Hanau quotes frequently from Leydig (8), whose histological 

 researches included the bird. His contributions extended from 

 1829 to 1873. Other writers mentioned by Hanau are : Ribbert 

 (14), MiAller (9), etc. Krukenberg (7) and Bogdanow (i) 

 investigated feather coloring and incidentally made some obser- 

 vations as to pigmentation of the skin. Kolliker (6) did con- 

 siderable work on the origin of the pigment cell, and Kerbert 

 (5) on the skin of vertebrates. Of comparatively modern 

 workers, Reichenow (12) on the skin of the legs and feet of 

 birds, and Gadow (2) on their general histology should be 

 noted. While some of these writers, particularly Hanau, dwell 

 to considerable length on pigmentation, none of them correlate 

 the pigmentation with the specific colors which occur in the 

 shanks of the different breeds of poultry. This paper is an 

 attempt to make such correlation. 



Methods. 



As this study was concerned with the color of the tissues, 

 methods were used which interfered, as little as possible, with 

 the natural condition of the skin. No technique which involved 

 the use of such fat solvents as xylol or absolute alcohol was 

 employed, save for the general histological work. Immediately 

 after dissection from the bird, the material was placed in a 

 weak solution of formalin, about 10%, where it was left until 

 required. Free hand sections were then cut and mounted in 

 liquid glycerine. This method has the advantage of preserving 

 the natural color of the pigment, and also of rendering possible 

 the cutting of sections thick enough to make the dilute oils 

 visible^ without the presence of a stain. Fat indicators, like 

 Sudan III do not discriminate between oils which are concerned 

 in giving color and those that are not. Nuclear stains render it 

 difficult to decide whether colored particles are pigment granules 

 or nuclear elements. A number of free-hand sections were sub- 

 jected to various stains, and were found valuable in certain 

 cases, as Sudan III in the study of yellow pigment, and eosin 

 for the location of blood vessels. 



For checking previous work on the general histological 

 structure the ordinary paraffin. and celloidin methods were em- 



