194 W. BALDWIN SPENCEE. 



cells are apparently undergoing degeneration, pigment being 

 deposited in them. 



Retina. — The hinder wall of th& vesicle forming the retina 

 is thinnest where it joins the lens and thickest posteriorly. 

 The whole is noticeable by reason of a great development of 

 pigment, which appears to surround all the elements. The rods 

 (R.) are very well marked and in some cases, especially in the 

 line of the optic axis, present the appearance of being striated ; 

 in the latter position also they are especially elongated. At 

 their external ends they seem to be connected with spherical 

 elements (n), also embedded in pigment ; these are united by 

 means of processes, rendered evident again by pigment deposited 

 upon them, with a layer of elements apparently corresponding to 

 the cone-shaped bodies of other retinas (Co.). In its most pos- 

 terior region the elements seem to be in connection with the fibres 

 of the optic stalk [Op. s.), which runs downwards and backwards 

 within the vacuolate tissue filling up the parietal foramen. 



Leioloemus tenuis. 



The external indication of the eye is very clear in the specimen; 

 the scale is in the usual position and surrounded by a series ar- 

 ranged in a circular manner around it as a centre, the two pos- 

 terior ones being larger than the other four. In the middle of the 

 eye-scale itself lies the circular cornea, white and dome-shaped. 

 Sections show that the eye is present beneath, the walls of the 

 vesicle being differentiated into a transparent cellular lens an- 

 teriorly and a retina posteriorly ; the rods are enveloped in pig- 

 ment, and the latter is deposited also through the whole thickness 

 of the retina. The whole organ had shrunk so much that it was 

 impossible again to do more than recognise the presence of the 

 structure, and the fact that it was differentiated into an eye ; the 

 proximal part of the epiphysis stretches, in the dura mater, very 

 nearly to the eye, but whether there is or is not any connection 

 between the two could not be determined. In this form also 

 pigment is present in great abundance in the skin, and its 

 absence above the eye is a marked feature in sections. 



