THE EYES OF THE BLIND VERTEBRATES OF NORTH AMERICA. 183 



cartilages in close contact with each other over the distal face. A third cartilage lay- 

 on the dorsal surface of the proximal part of the eye. The larger one of the two distal 

 cartilages measures 63 by 32 by 65 mi era, with a maximum diameter of the eye of 

 12 micrla. 



In a fish 33 millimetres long there were no cartilages on the proximal faces of 

 the eye. In the right eye there was a cartilage 128 micra long by 40 micra thick, 

 curved along the ventral part of the distal face. In the left eye there were two much 

 smaller cartilages on the distal face of the eye. 



In a fish 35 millimetres long there were two cartilages in the left eye placed as in 

 the fish 25 millimetres long, but they were larger. In the right eye the distal cartilage 

 was represented by two cartilages in contact with each other. 



From the above it is seen that the distal cartilage arises first (10 millimetre-stage), 

 the proximal ones not till much later (25- to 30-millimetre stage). The cartilages 

 did not reach their maximum size till later, and there is no evidence of degeneration 

 in them even in the oldest fish. 



The distal cartilage in older fishes is frequently nodular and lies in front of the 

 eye, where it was taken to be the lens by one of the earliest observers. In a spe- 

 cimen 90 millimetres in length a globular cartilage 62 micra in diameter lay just 

 over the pupil of the eye, which had a total diameter of 84 micra. One or other 

 cartilage not infrequently encroached on the general outline of the eye. 



In the left eye of an individual 105 millimetres long there were no traces of a 

 scleral cartilage; the right eye was not examined. 



In the right eye of an individual 108 millimetres long there was a single large 

 cartilage, 134 micra by 208 micra, lying at one side of the centre of the distal face of 

 the eye. 



In the right eye of an individual 123 millimetres long a minute cartilage was 

 found on the proximal face of the eye. It was not determined whether one occurred 

 over the distal face. In the left eye of the same fish a large cartilage lay over the 

 distal face (PI. XII, Fig. 8). 



In the left eye of the largest fish a single large cartilage 64 micra by 96 micra in 

 section occupies the region to one side of the distal face (Fig. 9). In the right eye 

 (Fig. 10) the distal cartilage measured 48 micra by 160 micra in section, and two 

 smaller proximal ones were also present, one of them 24 micra by 32 micra in section. 

 The scleral cartilages are the last structure to appear in the development of the 

 eye; they grow during the greater part of fife, and retain their structure to the end. 



