PTERYLOGRAPHY 59 



and hard-coated seeds. Branching from the oesophagus, between the mouth and the gizzard, 

 is the crop which serves chiefly as a storage pouch for freshly eaten material. At the junction 

 of the small and large intestines are attached two blind ducts or caeca several inches in length. 



As with birds in general, the two testes of the male are oval bodies lying on either side of 

 the backbone and against the forward portion of the kidneys on their lower surface. During 

 the breeding season these organs become greatly enlarged but at other times of the year may 

 be so small as to be difficult for an untrained observer to identify. In the female, the ovary, 

 resembling a bunch of grapes, occupies the same position as the testis. Normally, however, 

 only the left ovary develops in birds. It, too, becomes much enlarged during the breeding 

 season. 



Abnormalities of the sex organs are not infrequent. Thus, under certain conditions, the 

 ovary may wither on the left and the rudimentary organ on the right develop into a testis. 

 The effect on the plumage and other secondary sex characters is often remarkable. 



PTERYLOGRAPHY* 



The presence of feathers is one of the major distinctions of birds as a group. Among 

 the various species of the earth, wide modifications from the primitive type have developed. 

 Such differences, chiefly involving arrangement and types present, are used extensively in 

 studying evolutionary relationships. 



In the Appendix'^ is included a detailed account of the pterylography of the ruffed grouse, 

 of which the following is a brief resume. 



Although protecting practically the entire body, the feathers of a grouse, like those of most 

 other birds, grow in well defined areas called tracts rather than indiscriminately over the sur- 

 face. These tracts are bilaterally symmetrical and in them the feathers are usually arranged 

 in two series of rows, one at an angle to the other. This pattern can be easily seen in a 

 plucked bird. Tlie intervening areas of bare skin are termed spaces and are covered by feathers 

 situated in adjacent tracts. The development of such spaces in birds, as well as the restriction 

 of the feathers in tracts, undoubtedly facilitates better bodily efficiency through allowing great- 

 er concentration of blood vessels. The brood spot is principally a space although some 

 contour feathers are plucked by the hen along its outer edges. 



Of the many types of feathers found among birds, the grouse possesses neossoptiles. mesop- 

 tiles, teleoptiles, and filoplumes. Certain teleoptiles appear downy and are referred to as semi- 

 plumes, but true down feathers, or plumulae, are absent. Also, the neossoptiles which make 

 up the downy coat of the newly hatched chick are usually attached to the ends of the following 

 juvenile plumage, or mesoptiles. The teleoptiles are the typical feathers of the adult. 



An outstanding characteristic of the feathers of the grouse is the aftershaft — a second shaft 

 bearing most of the typical feather parts and attached near the base of the main shaft. It is 

 best observed among the contour feathers. 



* By John E. Trainer. 

 A See Appendix, p. 741. 



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