36 H. M. BERNARD. 



drawn, but later becomes filled with a rather loose tangle of 

 staining matter, composed mainly of the cytoplasmic frame- 

 work in which the nuclei were suspended. These phases not 

 only reveal the outward movement of the nuclei, but also show 

 that it is not due to pressure such as might be exerted from 

 a region of active division. The nuclei in these sections 

 can only have moved outwards under the action of some 

 attraction. This fact, that the force bringing about these 

 migrations is attractive, is important, though we cannot stop 

 at the present moment to develop it further. 



A slightly later phase in the formation of the inner 

 reticular layer can be seen in figs. 3 and 4. The irregulari- 

 ties seen in the layer in its first appearance, as a reticulum 

 filling up a split amongthe ranks of the nuclei, as just described, 

 have become more definable as tongues running out among 

 the outwardly pressing nuclei. In one case (fig. 4) several 

 tongues appear of nearly equal size, although the one which 

 appeared to be nearly in the axis of the eye was the largest. 

 In another case (fig. 3) this axial tongue was very much larger 

 than any of the others. As will be seen from the direction 

 of the arrows in this latter figure^ I explain these phenomena 

 as due to the migration of nuclei from the sides. The 

 attraction which first drew the nuclei from their original 

 positions in the embryonic retina to press outwards has 

 extended and drawn nuclei from the peripheral portions of 

 the retina which have not yet begun to function. Tliis com- 

 bined centripetal and outward movement of the nuclei would 

 naturally give the rudiments of the inner reticular layer the 

 shapes which they assume in these sections. That this 

 movement is taking place in the direction of the arrows 

 may be gathered from the closeness with which the iniclei 

 in these sections are packed in the central and inore actively 

 functioning region as compared with their straggling and 

 loose arrangement elsewhere. 



We have to add to this evidence, each item of which seems 

 fairly conclusive, the fact that the inner reticular layer grows 

 thicker as it slowly reaches the adult condition, and not 



