DEVELOPMENT AND STRUCTUHE OF TUE PINEAL EYE. 333 



vesicles, an anterior larger one, destined to becoixie the pineal eye, 

 and a posterior smaller one, the end of the epiphisis. In this 

 stage the nuclei of the columnar cells undergo karyokinesis, and 

 a second layer of cells is formed. In the next stage the anterior 

 vesicle becomes constricted off to form the Pineal eye. The further 

 changes in the eye are unknown, beyond tlie fact that it becomes 

 densely pigmented, and that an external modification of the scale 

 above fomns the so-called cornea. 



The stages of Himdia that I have had, have been from the 

 time when the eye is becoming differentiated from the epiphysis. 

 In the first stage the eye was seen lying close to the surface, being 

 separated from it only by a thin layer of connective tissue. The 

 eye is ovate in longitudinal vei'tical section, its long axis being 

 placed parallel to the long axis of the head of the lizard, and it is 

 slightly dorso-vent rally compressed. The lens is concavo-convex in 

 shape, the convexity being on the superior side. It is nearly the 

 •same thickness throughout, but slightly thinner where it joins the 

 retina. It is cellular in structure, and composed of two layers 

 of columnar cells. The retina is composed of seven layers. 



The first layer is composed of rods occupying about one-third 

 of the whole thickness. They have a distinct oval nucleus, and 

 taper at their inferior extremities. In the second layer are 

 spherical nucleated bodies, which do not stain deeply. They have 

 processes which run up to join the rods. 



Third layer. — Spindle-shaped bodies staining very deeply. No 

 nucleus could be detected, but they have processes which run up 

 to the rods and to the second layer of cells. Fourth layer.— A layer 

 of spherical cells similar to those of the second layer ; and also 

 triangular-shaped elements that stain very deeply ; these have 

 processes. Fifth layer. — Spherical cells as in the second and 

 fourth layers ; and a layer of spindle bodies similar to, though more 

 elongated than the third layer. Sixth layer. — A clear region 

 devoid of cellular elements, and having only a few cell processes 

 running across it. It may correspond to Spencer's molecular 

 layer. The Seventh layer is composed of connective tissue and 

 small nucleated bodies. The optic vesicle contains a humour. In 

 the next stage pigment is developed in the rods, and then in the 

 lower parts of the retina. No connection exists between the eye 

 in the later stages and the end of the epiphysis. On comparing 

 the forms which I have described, with those described by Spencer,* 

 the following are some of the points which are similar, or 

 dissimilar : — 



(1) A scale is modified to form a cornea in Gramniatopliora, 

 this being similar to such forms as Calotes, Varamts, etc. 



(2) The lens is doubly convex in outline, a point which appears 

 to be common to all the forms in which the eye is known. 



•Quart. Journ. Micro. Sdence, Oct., ISStJ. 



