254 



MR. W. P. PTCEAFT ON THE 



V. Ptertlosis or the Embeyo. 



Asio OTTJS, Linn. 



My embryos of this species may be divided into 3 stages, tbe last corresponding to 

 that of a 10-day chick. In this, only the rudiments of the contour-feathers have made 

 their appearance in the form of the characteristic bead-like papillae. 



Rio'ht side view of an embryo of Asio oins, showing the form of the pterylse. At this stage the pteryla colli 

 dorsalis closely invests the neck as in Sirix Jimnmea. The external aperture of the ear has not yet 

 reached its full size, and there are no pre- and postaural folds. The beak has not yet assumed its 

 characteristic curved shape. 



Stage III. 

 FterylcB : — 



Ft. ccqdtis. — The feathei'ing of the upper part of the head, as indicated by the 

 feather-rudiments, is very uniform, giving no sign of the differentiation into areas — 

 loreal, fronto-parietal, &c.— which appear in the adult. 



I n t e r r a m a 1 area as in the adult. 



Ft. colli dorsalis. — There are no lateral folds, the skin closely investing the neck, as 

 in StrLv Jlammea. 



Ft. spinalis as in adult. 



Ft. ventralis. — No outer branch is yet visible. 



Ft.femoralis. — As in adult, femoro-crural band strongly marked. 



Ft. cruralis. — No feather-rudiments have yet made their appearance on the podotheca. 



Ft. alaris. — The position of the future remiges, and nearly all the tectrices, are now 

 indicated, and the wing is seen to be aquintocubital. 



The external aperture of the ear has not yet reached its full development. There are 

 no opercular or postaural folds. 



Bhamphotheca. — Note the straight form of the beak and the absence of any indication 

 of a " cere." 



