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BLIND VERTEBRATES AND THEIR EYES. 



THE EYES OF STYGICOLA. 



The account of the eyes of Stygkola is based (i) on two young born October 

 20, each about 20 mm. long; (2) on the mother of the above, 92 mm. long; (3) on 

 various other older fishes, from 60 to 135 mm. long. 1 The early stages of the 

 development and the history of the eye between 20 and 60 mm. is not known. 



On October 30 I obtained a Stygkola at Alacranes. She gave birth to two 

 young on the evening of October 31, at Canas. They were born tail foremost. 

 The ovary of this specimen contained eggs 0.88 mm. in diameter, or nearly ripe. 

 The 2 young are referred to as 125 a and 125 b. 



The head of 125 b, seen from above, is represented in plate 25, figure b, and 

 the eyes are represented by plate 25, figure c. The eyes of the one born at Canas 

 (125 b) were symmetrical, nearly of the same size. The eyes moved, and as far as 

 I could judge were as readily movable as the eyes of other young fishes. 



The eyes were silvery, the argentea being apparently well developed. The iris 

 was well distinguished, the pupil too large for the lens, having a downward directed 

 notch continuous with the choroid fissure which is still visible as a pigmentless 

 streak. While small, there was nothing in the general appearance of the eye that 

 would lead one to conclude it might not be functional. 



The eyes are so placed in relation to the brain that a line tangent to their pos- 

 terior faces would be tangent to the anterior face of the optic lobes. This condi- 

 tion corresponds very well to the position in Lucifuga of equal size. 



Table of Measurements. 



1 From outer margin of scleral cartilage, unless otherwise stated. 



a From outside of pigment to outside of pigment. 



3 Total thickness of retina 67 n, as compared with 237 y. in Zygoneclcs. 



* These eyes lie 0.5 mm. below the surface, 

 s This eye lies 0.3 mm. below the surface. 



About the left eye of the second young (125 a) there was a large accumulation 

 of blood, which in section is seen to be in the choroid layer and mixed with the 

 orbital fat. Measurements of the eyes of the young, as well as of the mother, 

 are shown in the above table, and see also plate 25, G. 



1 A single larva obtained on September i, between 10 and 12 mm. long, is not well enough preserved to be 

 considered. 



