Jeffries.] 208 [February 7, 



diminished or, perhaps, arrested. The cells (fig. 5) divided off 

 from the mucous layer form a bed from one to three cells deep, 

 in nature the same as during the sixth day. The condition of 

 the mucous layer is unaltered. 



After hatching the epitrichial layer and some of the subjacent 

 cells dry up and are shed. Previous to this, the cells divided 

 from the mucous layer, which I shall call transitional cells, in- 

 crease in number, and the middle ones by a process of drying 

 and consequent shrinkage become the horn cells of the adult 

 skin. 



During the third week of incubation, or before, pigment cells 

 are apt to make their appearance in the mucous layer, and after 

 a few days to disappear. Since these cells are more abundant in 

 the appendages, as in the scutae and feather, descriptions of 

 them will be deferred till we come to those parts. 



The above description fairly embodies all the important con- 

 ditions of the developing epiderm as considered from a morpho- 

 logical point of view. The dates given for the various stages 

 are only apj)roximate. The development of the epiderm is very 

 irregular and eggs of the same age and from under the same hen 

 present marked differences. 



During the latter part of incubation the cutis vera is slowly 

 developed from the outer cells of the mesoblast. This is done 

 by the gradual growth of the vessels and nerves, each after their 

 own manner, and the transformation of other of the undiffer- 

 entiated cells into connective tissue and dermal muscles. Yet 

 some of the jn-imitive cells remain unaltered and form the con- 

 nective tissue corpuscles of the adult cutis vera. These, by 

 methods the same as in the embryo, develop into the elements 

 of the cutis vera and greatly increase its thickness and tenacity. 



DEVELOPMENT OF EMBRYO FEATHERS. 



The development of feathers is best divided into two parts, 

 that of the Irst feathers, which takes place during embryonic 

 life, and that of the feathers developed to replace those shed 

 during the moults. 



The development of the first feathers has been studied by 

 Engel(2) 1 , Pernitza (2) and Studer (16). The first author worked 



1 The numerals refer to the Bibliography at the end of this paper. 



