THE FEATHERS. 337 



of epithelial ridges is formed on them, and gives rise to the 

 permanent feathers, the development of which is essentially 

 similar to that of the down feathers. The permanent feathers, 

 as they are developed, gradually make their way to the surface, 

 replacing the down feathers, the nutrition of which is cut off by 

 further narrowing of the opening, or inferior umbilicus, at the 

 base of the quill. 



Feathers do not develop uniformly over the entire surface of 

 the body, but along certain definite lines or tracts spoken of as 

 pterylia, and separated from one another by naked areas or 

 apteria ; the actual arrangement of these feathered and feather- 

 less patches varying considerably in different groups of birds. 



List of the Trior e important Publications dealing tvith the 

 development of the Chick. 



Von Baer, K. E. : ' Ueber Entwickelungsgeschiohte der Thiere.' Konigsberg, 



1828, 1837. 

 Balfour, F. M. . 'The Development and Growth of the Layers of the Blasto- 

 derm ; and on the Disappearance of the Primitive Groove in the Embryo 



Chick.' Quarterly Journal of Microscopical Science, vol. xiii. 1873. 

 ' A Treatise on Comparative Embryology.' 1880-81. 

 Balfour, F. M., and Sedgwick, A. : 'On the Existence of a Head-kidney in the 



Embryo Chick, and on Certain Points in the Development of the 



Miillerian Duct.' Quarterly Journal of Microscopical Science, vol. xix. 



1879. 

 Balfour, F. M., and Deighton, F. . 'A Eenewed Study of the Germinal Layers 



of the Chick.' Quarterly Journal of Microscopical Science, vol. xxii. 1882. 

 Beard, J. : ' The Development of the Peripheral Nervous System of Vertebrates.' 



Quarterly Journal of Microscopical Science, vol. xxix. 1888. 

 Brandt, A. : ' Ueber den Zusammenhang der Glandula suprarenalis mit dem 



Parovarium resp. der Epididymis bei Hiihnem.' Biologisches Central- 



blatt, ix. 1889. 

 Budge, A. : ' Untersuchungen iiber die Entwickelung des Lymphsystems beim 



Hiihnerembryo.' Archiv fiir Anatomie und Entwickelungsgeschlchte. 



1887. 

 Cajal, E. : ' A quelle Epoque apparaissent les Expansions des Cellules Nerveuses 



de la Moelle Epinifere du Poulet ? ' Anatomischer Anzeiger, v. 1880. 

 Cazin, M. : ' Kecherches Anatomiques, Histologiqnes, et Embryologiques sur 



I'Appareil Gastrique des Oiseaux.' Annales des Sciences NatureUes, 



serie 7, tome iv. 1 888. 

 Corin, G., et Berard, E. : ' Contributions ^ I'^fitude des Matiferes Albuminoides 



du Blanc d'CEuf.' Archives de Biologic, ix. 1889. 

 Coste, M. . ' Histoire GSnfirale et Particuli^re du Developpement des Corps 



Organises.' Paris, 1847-59. 

 Davies, H. E. : ' Die Entwicklung der Feder und ihre Beziehungen zu anderen 



Integumentgebilden.' Morphologisohes Jahrbuch, xv. 1889. 



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