82 BULLETIN OF THE 



the method of the distribution of the nerve-fibres to the retinal layer. 

 It will require a more careful study of maceration-preparations in con- 

 nection with sections in different planes to settle this important question. 

 It seems to me improbable that the nerve-fibres pass directly through the 

 tapetura. From what I have seen, I think that most of them pass 

 around the margins of that layer to join the anterior ends of the retinal 

 •"•-ells, though I have reason to think that some of them reach the retina 

 through the fissure in the tapetum. 



The position of the other eyes is not quite so favorable for study by 

 means of sagittal sections ; and yet an examination of Figs. 4-6 is suffi- 

 cient to show that the infolding does not take place in the same direc- 

 tion in both of the lateral eyes. In the anterior laterals the retinal mass 

 lies in front of the infolding, whereas in the posterior laterals the retinal 

 mass lies, as in the posterior median eyes, behind the infolding. 



In the anterior lateral eye (Figs. 4, 5) the four tracts are readily dis- 

 tinguishable ; and it is necessary only to compare Figs. 4 and 5 with the 

 later stage in Fig. 15, and the still older one of Figs. 18 and 19, in order 

 to learn that the fate of each is the same as in the eye already described ; 

 a further description is therefore unnecessary. 



That all the layers — especially that producing the tapetum — are not 

 seen with the same distinctness in the posterior lateral eye, is, without 

 question, due to the direction of the axis of that eye. The sections are 

 cut in a plane which makes a considerable angle with the main axis of 

 the eye and of the infolding, and the figures therefore give a more ob- 

 lique view of the cells of the tapetal layer, which consequently are not 

 so readily distinguishable from those of the retina. The earlier sections 

 (Figs. 4, 5) pass through the fundus, — the last (Fig. 7) through the 

 margin of the infolding, where the first and the fourth layers begin to 

 merge into one another. (Compare Explanation of Figures.) 



It can be seen from the figures of a later stage (Figs. 13-15) that the 

 axis of this ocellus continues to be nearly perpendicular to the sagittal 

 plane. Of the three sections, that which is nearest the surface of the 

 head (Fig. 13) shows the greater portion of the tapetum,* with its 

 median fissure, nearly en face; there are also shown, between the ob- 

 server and the tapetum, faintly expressed markings nearly perpendicular 

 to the fissure. I could not discover that they were continuous across 

 the region of the fissure. They are undoubtedly due to the difierentia- 



* A part of the posterior end of this structure was cut away with the preceding 

 section. 



