DEVELOPMENT OF EYE OF SPARROW 285 



maj^ be due to individual variation, to different effects of the 

 reagents, or, more likely, to possible differences in the plane of 

 section. The column giving the thickness of the anterior layer 

 shows, after a slight increase, a progressive thinning. It is 

 interesting to note that with this reduction in thickness the 

 nuclei become less and less conspicuous. They either disappear 

 (which would explain the thinning) or are rendered transparent. 



The annular pad increases in thickness by the lengthening of 

 its cells. These cells are arranged radially at first and remain 

 so until after the beginning of the lenticular chamber (text-fig. 

 6, Lc). Soon after hatching the cells begin to show globular 

 projections from their inner ends as in the adult (Slonaker, '18). 

 The accumulation of these globules seems to exert a pressure 

 between the lenticular portion and the annular pad. By the 

 second day after hatching the lenticular chamber begins to appear 

 slightly posterior to the middle of the annular pad (text-fig. 

 6, U). This occurs at the line of junction of the two portions of 

 the embryonic lens. Separation occurs here because it is the 

 place of least resistance. The cells showing the most prominent 

 globular projections are adjacent to the forming chamber. All 

 of these cells are still straight and converge toward the center 

 of the lens. 



On the fourth day after hatching (V) the cells of the annular 

 pad have become longer and are beginning to curve posteriorly. 

 The lenticiilar chamber has increased and more cells show globu- 

 lar secretions or projections. The lenticular chamber is appar- 

 ently formed by the accumulation of this secretion. Since, in 

 its formation, it follows the line of junction of the two formative 

 layers, it may be said to correspond, in position at least, to the 

 original lens cavity. With increasing age these cells become 

 longer and more bent. Their nuclei remain in the peripheral 

 ends, leaving the inner portions of the cells filled with granules. 

 The lenticular chamber increases in size and seems to lag behind 

 as the center of the lens grows forward. This anterior growth 

 of the central part may in part be the cause of the bending of 

 the cells of the annular pad. 



