DEVELOrMKNT Ol .lACANA 25)9 



period, of much greater size than it is today. ''IMiiis we can 

 inini>ine an ancestral l)ird witli clawed tlninil) and tinker tliat 

 nested in trees; probably with a str()n<>er Hi^»ht, and cei'tainly 

 with a better l)alanced and longer tail than at present. 



DIASTATAXY 



A crowdino- and i-e(hiction of the f'oni-th seeon(hn-y oc- 

 curs in the youn<»' chick, which in sonic way may be due to 

 the diastataxy of the win*);'. There are ten secondaries and 

 eleven coverts in the einbi'yo, the extra covert being- placed 

 l)etween the I'ourth and fifth. It is small and raised slightly 

 out of Hue from the others, there also being a slight shifting- 

 out of })lace of the one above. Here, however, the shifting 

 ap])ears to cease and the coverts above remain in their regu- 

 lar positions. 



At hatching time or a little later, the extra covert falls 

 di]"ectly into line and now regularly becomes the fifth, while 

 the original fifth becomes the sixth, and so on. There is, 

 however, no fifth secondary to which it may become a covert. 

 All the down secondaries are in line. (Fig. 98.) 



Now comes a curious phase in the growth of the secon- 

 daries themselves. As they commence to grow rapidly, the 

 fourth is left far behind as a mere little bud, crowded and 

 pushed up out of line as was once the extra covert. After 

 a period it manages to regain the line and, at first very slowly, 

 to lengthen. Later, however, when the secondaries are near- 

 ly grown it more than recovers the strength it once lost and, 

 pushing quickly ahead, overtakes the rest before they are 

 fullv matured." (Fig. 98.) 



It is hard to account for this condition, though the dias- 

 tataxy of the wing may have something to do with it. It 

 is possible that some particular stress exerted by the move- 

 ment of the changing coverts, may have caused it to be drawn 

 up, though why the down slieath should be in line and not 

 the main sheath, can be answered onlv bv a more thorough 



