562 



Mr. W. B. Spencer. 



[June 10, 



distal portion of the epiphysis, which becomes completely separated 

 off from the proximal portion of the same, and lies completely sur- 

 rounded by connective tissue in the parietal foramen. If in contact 

 with a nerve, as frequently happens according to Graaf in Amphibia, 

 then the nerve in question is a subcutaneous branch of the ramus 

 supramaxillaris of the trigeminal. 



It is difficult to imagine why a single medianly placed organ should 

 be supplied in any way by a branch from one only of two paired 

 lateral nerves. 



The two most important facts established by the present series of 

 observations are — 



(1.) That Leydig's " frontal organ" exists as a structure comparable 

 to an invertebrate eye, widely distributed amongst Lacertilians. It 

 may, in reference to its position and structure, be perhaps best called 

 the pineal eye. 



(2.) That the eye is connected by a medianly placed nerve with the 

 proximal portion of the epiphysis, and thus with the dorsal surface of 

 the brain in the median line. 



There can be further little doubt that this nerve is the remains of 

 the part connecting the distal with the proximal part of the epiphysis, 

 that it is in other words formed as the optic nerve from a hollow 

 outgrowth of the brain, which subsequently becomes solid. 



The structure of the eye in two or three typical cases is as 

 follows : — 



(a.) Hatteria. — In this form the organ is well developed, and being 

 through Prof. Moseley's kindness enabled to procure a fresh specimen, 

 it has been possible to determine the elements comprising the optic 

 vesicle. 



In all the eyes yet examined a lens is present. Yon Graaf figures 

 it in Anguis as separated from the hinder part of the vesicle, but this 

 does not hold good for any of those examined during the course of this 

 work. The lens, on the contrary, appears to be only the modified 

 anterior portion of the optic vesicle with the hinder walls of which 

 it is directly continuous. In Hatteria it is somewhat cone-shaped, 

 with a broad base corresponding to the anterior surface of the vesicle ; 

 it is distinctly cellular, the nuclei being well marked, and the cells 

 having a definite arrangement. 



The walls of the vesicle posterior to the lens consist of the following 

 elements : — (1.) A layer of rods bordering the vesicle internally, 

 deeply imbedded in dark pigment, arranged as seen when the rods are 

 separated so as to give the latter a clearly marked striated appearance. 

 (2.) External to these is a layer composed of rounded nucleated 

 elements, two, and in fact possibly three, rows deep. (3.) External to 

 this what may be called a molecular layer, consisting of finely punc- 

 tated material, through which seems to run a supporting structure ; 



