296 JAMES ROLLIN SLONAKER 



During the two days following hatching very rapid changes 

 occur in the pecten. At two days of age it has ten folds and has 

 become almost as thin as the adult pecten (fig. 84, P). Four 

 days after hatching the number of folds has increased to eighteen. 

 At this age the first pigment granules appear. They are scat- 

 tered in the tissue near the surface of the tip or free margin, 

 which becomes in the adult the crest. 



At the age of six days after hatching the pecten has practically 

 reached the form of the adult (fig. 93, P). The twenty folds, 

 the number in the adult eye, can be easily distinguished. The 

 pigmentation, however, is not complete. 



There is quite a difference in the relative time of the appearance 

 of the folds of the pecten in the chick. Nussbaum ('01) finds 

 the number in the eleven-day chick embryo to be seven and in 

 the thirteenth-day to be seventeen. Kessler (77) found, in the 

 twelve-day chick, fifteen distinct folds, the middle one being 

 the longest. In the seventeen- or eighteen-day embryo he says 

 the folds are the same in number as in the adult. Huschke 

 ('35) gives the number of folds in the hen as seventeen. 



As stated above, the pecten in the six-day sparrow has reached 

 the adult condition, with the exception of its pigmentation. 

 Pigment granules were first seen in the crest of the four-day 

 sparrow. At the sixth day the crest is more densely pigmented 

 and there has been a progressive pigmentation from this region 

 down the angles of each fold toward the base. This is most 

 pronounced near the crest, gradually grows less toward the base, 

 and disappears at about one-third the distance from the crest 

 to the base. Everywhere the pigment appears as small granules 

 which have a uniform and even distribution. The greater 

 pigmentation of one region over another is thus due to a closer 

 arrangement of these granules. 



This spreading continues, and by the tenth day after hatching 

 a very few pigment granules are found in the proximal region. 

 In the meantime the granules have become more numerous in 

 the other portions, and, in the crest, have begun to arrange 

 themselves into groups similar to the adult condition. 



