148 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Professor Mark for the encouraging interest he has shown in my inves- 

 tigations, for helpful suggestions, and for invaluable training in precision 

 of method. 



In the course of my histological studies on the developing feather I 

 have naturally examined the literature of the subject, and believe tliat 

 a more elaborate analysis and description of the various stages in tlie 

 development of the complex structure of the feather, especially of those 

 elements producing color, is highly desirable. This work therefore deals 

 mainly with the histological side of the subject of color in the definitive 

 feather with some contributions to the general knowledge of the 

 development of the feather. 



II. Methods and Material. 



My principal material has been obtained from the remiges of Sterna 

 hirundo Linn. During the summer of 1899 while occupying a table in 

 the laboratory of the United States Fish Commission Station at Wood's 

 Hole, Mass., I obtained two young birds of S. hirundo with feather 

 germs (" pin feathers "), some of which had begun to expose fully corni- 

 fied portions at their ruptured distal ends. 



Immediately after killing the birds, the wings and strips of skin 

 bearing feathers were placed either in Kleinenberg's picro-sulphuric 

 mixture, or saturated aqueous solution of corrosive sublimate. 



In the summer of 1900 I put up some more material of S. hirundo, 

 this time using Kleinenberg's picro-sulphuric fluid and the fixing 

 mixtures of both Hermann and Flemmi ng. T found that better pene- 

 tration was secured when the feather was simply pulled from the 

 feather follicle and dropped into the fluid, without the superfluous 

 tissue of the follicle and the connective tissue below the inferior 

 umbilicus. One soon learns to perform this operation easily and 

 without injury to the tissues, in spite of the fact that the latter are 

 very delicate at the proximal end of the feather germ. 



I have found Kleinenberg's picro-sulphuric mixture and Hermann's 

 fluid the most satisfactory fixing agents; the latter gives by far tlie 

 best preservation. Kleinenberg's picro-sulphuric is especially advanta- 

 geous for the study of developing pigment cells, in that it leaves no stain 

 after proper washing, whereas osmic-acid fluids produce- a blackening of 

 the cytoplasm that is very objectionable in the study of early stages 

 of the pigment cell. 



