458 



find only three kinds of histological elements: 1) radial supporting 

 fibres, 2) ganglion-cells and nerve-fibres, 3) sense-cells. 



The radial supporting fibres are comparable to the Müller's fibres 

 in the lateral eyes, and probably extend right through from surface to 

 surface of the retina, their inner ends forming the well-developed 

 internal limiting membrane, and their outer ends abutting against 

 the inner capsule of the eye. Their nuclei appear to be all lodged in 

 their outer portions, which have the misleading appearance of a layer 

 of short conical cells. 



The ganglion- cells are numerous, and are readily distinguished 

 by their large spherical nuclei, finely granular cytoplasm (with usually 

 one large projection), and the shrinkage cavity which surrounds 

 them. 



The sense-cells are slender, elongatedly spindle-shaped, with large 

 oval nuclei. Their outer ends run into the layer of nerve-fibres. 

 Their inner ends project slightly into the cavity of the eye, but are 

 covered with little conical caps, formed apparently by extension of the 

 internal limiting membrane. 



In most respects the structure of the retina agrees closely with 

 that of Anguis and Lacerta as recently described by Nowikoff. That 

 author, however, gives a somewhat diflerent account of the projecting 

 ends of the sense-cells and of the distribution of the pigment. 



Baldwin Spencer considered that in Sphenodon the pigment was 

 especially associated with the sense-cells; Nowikoff, on the other hand, 

 maintains that in Angius and Lacerta the pigment is lodged in the 

 radial supporting fibres. According to my own observations on Sphen- 

 odon, the pigment granules lie between the various constituents of 

 the retina, and are brought in from outside the eye by wandering 

 pigment cells. Such cells are abundant in the connective tissue around 

 the eye, between the inner and outer capsules, and sometimes they 

 also occur in the form of pigment-balls in the cavity of the eye itself, 

 having apparently passed through the retina without breaking up and 

 discharging their contents, usually, however, they appear to break 

 up in the outer part of the retina, and the granules which they con- 

 tain stream in in radial lines and streaks between the radial fibres and 

 sense-cells, to such an extent as greatly to obscure the histological 

 structure of the retina. The wandering pigment-cells may possibly 

 obtain their pigment granules from the very large stellately branched 

 pigment cells which lie in the dura mater outside the capsule of the 

 pineal eye. 



The pigment is especially abundant towards the margins of the 



