208 



BLIND VERTEBRATES AND THEIR EYES. 



THE EYES OF LUCIFUGA. 



The snout of Lucifuga is broad and depressed to the posterior edge of the max- 

 illaries — duck-bill shaped. The eye is distinguished without difficulty in the trans- 

 lucent living individuals, and even in specimens preserved in formalin or alcohol 

 it is readily distinguished up to very old individuals. 



In the older specimens the skin over the eye readily discloses the location of 

 the organ. There is over the eye in these specimens a hemiovate elevation sepa- 

 rated from the rest of the skin of the head by a distinct groove. The skin in this 

 ovate arch is not any less abundantly supplied with pigment than any other part 

 of the head, and there are no other distinguishing features to indicate that it is 

 better adapted to admit light than any other part of the skin of the head. In 

 some cases it is even more densely pigmented than neighboring regions. The 



region is proportionately larger 

 o 



in young individuals than in old, 

 but is more conspicuously de- 

 marked in the older than in the 

 young. 



Removing the skin shows 

 that beneath the ovate arch lies 

 a mass of orbital fat, approx- 

 imately in the center of which 

 the eye lies embedded. The 

 orbital fat-mass seen from above 

 has an oval shape, considerably 

 longer in the axis of the head 

 than transversely. Behind, the 

 mass touches the orbital process 

 of the frontal bone. The eye is 

 placed approximately over the 

 middle of the maxillary. 



The proportion of the or- 

 bital space or socket occupied by the eye differs greatly in individuals of 

 different sizes. In younger individuals, just about to be born, the eye fills a 

 large part of the socket (plate 16, fig. b), while in the old it forms an insignificant 

 dot in a mass of fat and connective tissue, hundreds of times larger than the eye 

 (plate 21). The relation of the eye to the surface is similarly conditioned with age. 

 In the young it lies near the surface, while with age it becomes farther and farther 

 removed, retaining however its relative position in the orbital fat-mass until old 

 age, when possibly it may move nearer to the skull. 



Seen from the surface, that is without sectioning, the eye presents great fluctu- 

 ations in size. These are in part conditioned by the size of the individual, but in 

 part are independent of size. Other things being equal, the eye decreases in size 

 progressively from birth to its disappearance in extreme old age. This process is 

 accompanied by, if it is not responsible for, the appearance of pigment masses. 

 These are either intimately associated with the eye, as in the development of great 



Fig. 72. 



(A) Outline Camera Drawings of Eye of 4 Young of Female shown in plate 

 15 C from Sides, Left Eye on Left, Right Eye on Right, so that Middle of 

 Pairs is Anterior, a. Fish 18 mm. long; 6, 18.5 mm.; c, 10 mm.; d, zo 

 mm. For details of these Eyes see figs, plates 16 to 18, 16 mm. and 4. 



(B) Eyes of Mother of 4 Young, shown in A, drawn to Same Scale; 0, from 

 above; 6, from sides. For sections, see plate 21. 



(C) Outlines of Eyes of No. 05. a. Fish 53 mm. For sections see plate 20 

 c and plate 24 a, 16 mm. and 6. 



