Jeffries.] 232 [February 7, 



The setae are developed as papillae of the cutis vera (fig. 30), 

 which at first are indistinguishable from the feather papillae, but 

 never become sunken. They appear on the posterior edge of the 

 dorsum of the tongue about the seventh day, and then gradually 

 spread over the surface of the mouth and fauces. 



About the twelfth day horn cells appear and keep on forming, 

 so by the eighteenth day we have what may be regarded as the 

 perfect seta of embryonic life (fig. 28), with the following layers, 

 epitrichial, granular, horn, transitional and mucous. These are 

 all so exactly like the rest of the body that it is only necessary to 

 refer to the figure. 



I have carefully sought in ducks and hens of all ages for any 

 resemblance between the mouth papillae and feathers ; in no case 

 have I found the least resemblance between the two. Nor, so far 

 as my observations go, do small papillae run together and form 

 large ones. 



Though properly beyond the province of this paper, it may not 

 be amiss to take a hurried glance at the development of the 

 glands of the epiderm. These are confined to the inner surface 

 of the head, the oil-gland and the cloaca. Of the glands of the 

 cloaca I can say nothing. 



The mouth glands all originate as solid ingrowths of the deeper 

 layers of the epiderm, with subsequent formation of a lumen and 

 duct, in the same manner as the mucous glands in the vertebrata. 

 The epitrichial layer plays no part. 



The long gland on each side of the tongue, in the floor of the 

 mouth is formed, according to Gotte (24) by a number of mucous 

 glands opening into a longitudinal furrow in the floor of the 

 mouth. Besides glands crypts are to be seen in the tongue of 

 ducks, these are formed as simple insinkings of the epiderm. 



The oil-gland is formed, according to Kossmann (25), by two 

 insinkings of the epiderm, and then the development of glands 

 from the epiderm of the pit. That is, very much as in the sub- 

 lingual glands. 



Here it is of interest to note that there is absolutely no differ- 

 ence between the first stages of a mammalian hair and the small 

 glands of a chick or mammal, yet few would consider hairs and 

 glands homologous structures. 



