EYE OF LUCIFUGA. 



211 



occurs and where it is abundant. This makes it seem probable that the young of Slygifola live in 

 deep water and are not found in the open sink holes or that their habits otherwise prevent them 

 from being found. 



One more element tends to show that all the young are Lucifuga. Lucifiiga differs from Stygicola 

 in the shape of the nape, the scales of the head, the teeth, and the number of fin-rays. These char- 

 acters in the young were always those of Lucijuga as far as could be made out. 



With these preliminary remarks the details of the structure of the eyes of differ- 

 ent individuals may be given. The different parts of this account may be begun 

 with a description of the conditions obtaining in the 4 young and their mother 

 (referred to as 76) since there can never be any question concerning the genetic 

 relationship of the eyes. 



THE EYE MUSCLES. 



The six normal eye muscles are all present in the young of 76, both in those with 

 a large eye and those with a small eye. The muscles in one of the large-eyed 

 specimens and one of the small-eyed specimens have the following maximum 

 diameter : 



These muscles can all be traced quite readily from their origins to their inser- 

 tion (plates 16 to 18, msc.) and are apparently quite normal. 



In the mother of these young the oblique muscles can be very readily traced 

 in the socket in front of the eye, but their insertion in the eye is by fibers bent 

 nearly at right angles. 



The dorsal, ventral, and posterior rectus of the left eye can be traced from 

 their origin to their insertion. The posterior rectus is an exceedingly slender 

 thread, and with the ventral rectus diverges from their origin, they converge again 

 at their insertion. The dorsal and ventral recti are merged with the oblique 

 muscles so that they appear as continuous strands, with the fibers mentioned 

 above diverging from their union. (See also plate 22, fig. c.) 



In the right eye the posterior rectus is attached to the eye independently, the 

 ventral rectus and oblique are much more remote from the eye than in the left eye 

 at the point where the connecting fibers are given off to the eye. 



In one of the largest individuals, 93 mm., the oblique muscles can be seen in the 

 socket, but I have not been able to connect them with the eyes. The dorsal and 

 ventral recti are present and possibly the posterior rectus. The muscles are, in 

 other words, not so very different from those in 76. 



THE SCLERA. 



The sclera is most highly developed in the eyes of unborn young about 20 mm. 

 long. It is well developed, with its cartilages, in 12 mm. young. Its most striking 

 feature is the large scleral cartilage. This in the young 20 mm. long is a segment 

 of a hollow sphere with a large opening for the iris. The edges of the proximal 

 opening are at times curved in. It resembles a convex shield with an opening in 



1 The four young specimens bear the serial numbers 76, a, b, c, and d. 



