206 W. BALDWIN SPENCEE. 



the paired eyes, and is easily discernible in the living animal, 

 one of which I was enabled to examine. It consists of a dark 

 patch, having again the appearance of a membrane stretched 

 tensely over a cavity, surrounded by an irregular, slightly- 

 raised, white border, represented in the figure, in which is 

 drawn only the central part of the scale. 



Thus the modification to form a ^'cornea" is, as reference to 

 the figure will show, in a rudimentary state, and foreshadows 

 the similarly rudimentary condition of the organ beneath. In 

 fig. 29 is represented a solid side view of the brain, showing 

 the position of the pineal gland ; it lies enclosed in the brain 

 membranes, and fitting closely into the parietal foramen, out 

 of which it is easily removed along with the dura mater. The 

 epiphysis is very long, and stretches far forward beyond the 

 roof of the thalamencephalon, almost to the anterior extremity 

 of the cerebral hemispheres, its distal extremity being deeply 

 embedded in pigment in the dura mater, and having the 

 appearance, as in fig. 29, of a dark, swollen mass. 



In section it is seen that the epiphysis is hollow throughout 

 its whole course, the cavity being in direct communication 

 with the third ventricle ; the cells composing its walls are all 

 columnar in nature and distinctly nucleated, cilia also being 

 easily distinguished in most parts. 



The whole may be divided into two parts : (1) a proximal 

 portion, stretching from the roof of the thalamencephalon in 

 the form of a tube to the parietal foramen ; and (2) a swollen 

 distal extremity lying in the latter, and closely invested by 

 vacuolate tissue. In other words, the epiphysis in Cyclodus 

 has the form of a vesicle attached to the brain by a 

 hollow stalk. The vesicle may be regarded as homologous 

 with the eye of other lizards in a rudimentary state,^ and the 

 hollow connecting process with the solid pineal stalk and 

 proximal part of the epiphysis of such a form as Hatteria. 



In figs. 19 and 20 is represented, on a larger scale, the 

 str«cture of the anterior and posterior walls of the vesicle (by 

 the anterior wall is meant that nearest the external surface). 



^ It may also be closely compared with the condition in adult Elasmobranchs. 



