DEVELOPMENT OF THE EYE OF AMBLYOPSIS. 159 



The development of these cartilages to such unexpected size indicates that these 

 cartilages are self-determining and not conditioned by the stimulus to growth by 

 the eye with which they are in contact. In the right eye of this fish there were 

 two cartilages in close contact with each other over the distal face. A third car- 

 tilage 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 ll, with a maximum diameter 

 of the eye of 12 jx. 



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

 eye. In the right eye there was a cartilage 128 ll long by 40 ll 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 mm. long there were two cartilages in the left eye placed as in 

 the fish 25 mm. 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 mm. stage), 

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

 not reach their maximum size till later. 1 



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 

 specimen 90 mm. in length a globular cartilage 62 /a in diameter lay just over 

 the pupil of the eye, which had a total diameter of 84 ll. One or the other car- 

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



In the left eye of an individual 105 mm. long there were no traces of a scleral 

 cartilage; the right eye was not examined. In the right eye of an individual 

 108 mm. long there was a single large cartilage, 134 ll by 208 ll, lying at one side 

 of the center of the distal face of the eye. In the right eye of an individual 123 mm. 

 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 (plate 10, fig. r>). 



In the left eye of the largest fish a single large cartilage 64 ll by 96 ll in sec- 

 tion occupies the region to one side of the distal face (plate 10, fig. d). In the right 

 eye (plate 10, fig. f) the distal cartilage measured 48 /a by 160 ll in section, and two 

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



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

 the eye ; they grow during the greater part of life and retain their structure to the 

 end. 



THE HISTORY OF THE OPTIC NERVE. 



The details of the formation of the optic nerve have not been followed. No 

 indications of it were seen in the eyes of the embryos 4.4 mm. long. In the eyes 

 of embryos 5 mm. long it is well developed, forming a solid strand of fibers 12 ll 

 in diameter which is readily traceable to the brain. The optic nerve increases 

 but little, if any, after its formation. Its development is rapid. In subsequent 

 stages it is not always traceable from all the cells forming the ganglionic mass. 

 In the 6-mm. larvse its fibers were distinctly traceable from the cells nearest the 

 choroid fissure, while in later stages they were more distinctly traceable from the 



1 In the original the words " and there is no evidence of degeneration in them even in the oldest fish " 

 completed the sentence. This is not strictly true and is omitted. 



