7^6 THE PTERYLOGRAPHY OF THE RUFFED GROUSE 



it is relatively small and. on the inner surface, is entire!) missing, while on the ouler side 

 it is continuous with the lateral s])a((> of the trunk. 



The functions of the spaces have been described above when quite deliniteU accepted. 

 Some, however, are without any definitely known function. For several of these, possible 

 explanations present themselves. For example, certain spaces of the head and the inferior 

 space occur on protruding bones. It is generally conceded that these spaces provide a smooth 

 contour but possibly the bones pressing against the skin hinder an adequate blood supply. 

 Again it is probable that a number, such as the spinal space, facilitate increased efficiency 

 through allowing greater centralization of the blood vessels supplying the feather tracts. 



The Brood Spot. This might also be considered as a space. In order to incubate the usual 

 clutch of eggs, practically the whole under surface of the body is plucked of feathers. All 

 feathers, regardless of size, are removed except, apparently, the hair feathers. The area 

 plucked roughly includes the last four rows of the sternal and axillar regions and extends 

 from there almost to the anus. Often the forward edge is irregular. On the legs, all of the 

 area which could come in contact with the eggs is plucked. 



The Feathers 



The feathers of any bird comprise a variety of types modified for divers purposes and 

 differing widely between species. Those found in the ruffed grouse are described, as well 

 as what little is known concerning total number and variations with sex and season. 



Types. The feathers which make up the downy coat of the newly hatched chick are re- 

 ferred to as neossoptiles, being characterized by the presence of pigment and the absence of 

 a shaft. They range in length from 2 to 14 mm. With certain exceptions, the neossoptiles 

 are followed by the juvenile plumage, a fact which has led to the application of the term me- 

 soptiles to the latter. In addition to their manner of development, a weaker, lacier appear- 

 ance and pale coloration also distinguish the mesoptiles from the typical feathers or teleop- 

 tiles of the adult. 



Filoplumes are the so-called hairs, actually highly modified feathers. They are distributed 

 generally over the body and can be readily identified growing from the elevations of the skin 

 surrounding the bases of the ordinary feathers. 



Plumulae, or true down feathers, are characterized by the absence of both a central shaft 

 and i)igment. They are. strictly speaking, entirely lacking in the ruffed grouse although a 

 number of small semiplumes have the superficial appearance of plumulae. Such feathers 

 are found in the various spaces and among the coverts of the wings and tail. 



The tyjjical feathers are the teleojjtiles coni|)rising the rectrices. remiges. their coverts, and 

 the general contour feathers. Basically, each consists of an inner, fluffy portion for warmth 

 and an outer flat, stiff portion, but variations range from the almost completely pennaceous 

 rectrices and remiges to the almost completely downy feathers found anterior to the anus. 



Many of the highly modified leleoptiles are functional although some are probably only 

 vestigial. Those of the evelids serve as small eyelashes. The feathers of the tuft on the oil 

 gland are without a central shaft and are greatly weakened. The auriculars covering the ear 

 openings are specially adapted for the purpose of protecting the ear without interfering 

 with hearing to any extent, the stiff shaft lu-aring very few barbs. 



Com|)leteK (li>«n\ Icicdptiies are (]nile numerous and are frequentl\ reft i red to as semi- 

 plumes. Unlike tile true down feathers, the) possess a central shaft. Seldom are they exposed 



