190 W. BALDWIN SPENCER. 



Monitor (sp. ?). — In the Monitor examined there was no 

 external trace of the organ to be discerned, though when the 

 skin was removed from the dorsal surface of the head and 

 viewed by transmitted light, an absence of pigment and 

 general transparency in the spot overlying the parietal foramen 

 indicated the position of the eye. The latter could be easily 

 distinguished as a small black spot lying within the foramen, 

 which was itself, in the form examined, extremely small. 

 Unfortunately the specimen was in a bad state of preservation 

 histologically, and the tissues very dry, so that it was again 

 impossible to make out the details of the structure. The 

 eye, which is deeply pigmented save anteriorly, where is the 

 lens, appears to be placed at the distal extremity of a pineal 

 stalk which, as in Varanus giganteus, runs up vertically 

 through the foramen, accompanied as usual by a large artery. 



Chameleo vulgaris, PI. XVI, fig. 21 ; PI. XIX, fig. 40 ; 

 PI. XX, fig. 6. 



In this form a curious modification takes place, an optic 

 vesicle being formed but not reaching any high degree of 

 development. In the short account written in ' Nature,'^ it 

 was stated in a note that the organ was present in Chameleo 

 vulgaris — a statement of which de Graaf has subsequently 

 denied the truth. He says that though the parietal foramen 

 is open in the young form it becomes closed as the adult state 

 is reached, and that there can be thus no organ remaining in 

 connection with the proximal part of the epiphysis. Before 

 reading his note, and subsequently to the publication in 

 'Nature,' three more adult specimens were cut in section 

 (the first note was based upon a dissection), with the result 

 that each one has fully confirmed the statement that the organ 

 is present in Chameleo, and moreover remains in connection 

 with the proximal part of the epiphysis, though it certainly is 

 in a comparatively low state of development. 



External Indication. — The presence of the organ is 

 indicated in both Chameleo vulgaris and Chameleo 

 ' 'Nature,' May 13th, 1886. 



