54 KINGSLEY. [Vol. I. 



The origin of these, I have not determined. Beyond the second 

 of these gangha is a second fibrous portion, which connects the 

 visual organs and the optic gangha with the brain. This con- 

 nection did not exist in the earUer stages, but I am unable to 

 say whether the fibres grow out from the supra-cesophageal gan- 

 gHon or from the nervous rudiments of the eye. It should be 

 mentioned that the rows of ganglionic nuclei at this stage are 

 opposite the crystalline cones, and alternate with the rows of 

 retinal nuclei. 



Fig. 8 is a portion of the eye of the same stage still further 

 enlarged, but taken a little further back. It shows the first 

 appearance of the pigment, which is plainly not of mesodermal 

 but of epidermal origin, arising from the retinogen. The cell- 

 outlines are very indistinct ; but it is evident that the pigment is 

 deposited first in the inner ends of the inner cells of the retinal 

 rows, or those which form the outer wall of the optic cavity. 

 The same figure also shows more clearly the distinctness of the 

 epidermal layer, and also that the crystalline cone is divided 

 through the middle. At this stage, however, one cannot see 

 which of the cells arising from the retinogen are concerned in 

 the secretion of the cones ; but this point becomes apparent at 

 a later stage, when the embryo is nearly ready to leave the Q^'g. 



Figs. II, 13, and 10 will explain the various processes involved. 

 They are taken from an embryo in which the yolk has become 

 nearly absorbed, and in which the optic stalks have begun to 

 bud out. Fig. 1 1 is an actual section, which is diagrammatic 

 only in that it omits, for clearness, a part of the pigment. Fig. 

 10 is drawn from stained and teased sections, and shows the 

 shapes of the cells of the retinogen. Fig. 13 is a diagram con- 

 structed from both of them. It contains, however, nothing 

 which I have not clearly seen. At this point it is necessary to 

 add some terms for the various portions, and I have adopted 

 the terminology introduced by Patten ('<?<5). The epidermis 

 cells (^) are now distinct from those of the retinogen, and 

 have begun the secretion of the cuticula, which is modified 

 into lenses (/) over each crystalline cone. The extension of the 

 cell protoplasm across the end of the crystalline cone, as repre- 

 sented in Fig. 13, is not certain. It does, however, take such a 

 position in later stages (after hatching), and so I have introduced 

 it into the diagram. In the rows of retinal nuclei there has 



