DEVELOPMENT OF EYE OF SPARROW 275 



easily be traced over the ciliary bodies as a non-pigmented layer 

 to the periphery of the iris. The curvature of the cornea has 

 greatly increased so that the aqueous chamber has the same shape 

 as in the adult. 



By the fourth day after hatching all these structures have 

 reached a development similar to that of the adult except the 

 ciliary muscles and the muscles of the iris. These are not 

 completely striated until a few days later, when the bird is about 

 to leave the nest. 



The development of the cornea, the aqueous chamber, and the 

 iris of the duck and the crested grebe has been studied by C. 

 Lindahl ('15). In general, the development of these structures 

 in the sparrow corresponds with his descriptions in these birds. 

 Some differences are noted in the age at which certain parts 

 appear. These I attribute to the differences in the periods of 

 incubation of these birds. He has found similar discrepancies 

 in the tW'O birds studied. 



We both agree that, with the exception of the epithelial layer, 

 the cornea is derived from the mesenchyme; that the membrane 

 of Descemet appears first and is soon foUow^ed by a gradually 

 thickening substantia propria; that the aqueous chamber, at first 

 confined to the angle at the peripheral portion of the iris, increases 

 in size by an increase in the curvature of the cornea; that the 

 iris is developed mostly from the mesenchyme, the retinal and 

 pigment layers forming only a thin densely pigmented layer 

 adjacent to the lens; and that the ciliary bodies are developed 

 from the retinal and pigment layers, and from the undifferen- 

 tiated chorioid, or mesenchymatous cells, the latter forming 

 their main bulk. 



The first appearance of the sphincter and dilator muscles of the 

 iris is at about the time of hatching. They occur as denser areas 

 in the posterior portion of the stroma. From my sections it is 

 impossible to state whether they are mesenchymal or ectodermal 

 in origin. According to Keibel and Mall ('12), these muscles 

 are of ectodermal origin in man and that they take their origin 

 from the iridal portion of the outer layer of the optic cup at about 

 the twenty-fourth to the thirtieth week of fetal life (Heerfordt, 



