170 THE EYES OF THE BLIND VERTEBRATES OF NORTH AMERICA. 



caves with some 180 acres of land about their entrances have become the property 

 of Indiana University. 



I am indebted to Dr. Jacob Reighard, under whose direction Mr. Lewis H. Weld 

 made a series of photographs of entire eggs and embryos for me, and to Professor 

 D. W. Dennis, who prepared the photomicrographs of the eyes. 



II. EARLIER WORK ON THE EYE OF AMBLYOPSIS. 



In a former paper (Eigenmann, '99) I gave an outline of the work done by pre- 

 vious authors and described the structure of the adult eye of the species under 

 consideration and also the eyes of the related species of the Amblyopsidse inhab- 

 iting the caves and surface streams of the Mississippi valley and the Atlantic slope 

 of North America. It was found that the different members of the family have eyes 

 in different stages of degeneration, from the eyes of the various species of Chologaster, 

 which are nearest the normal, to those of Troglichthys, which are the most degenerate 

 eyes of any vertebrate yet described. The eye of Amblyopsis, the species now under 

 consideration, reaches a maximum diameter of about 200 micra, with an average of but 

 143 micra. This eye is practically without vitreous body or vitreous cavity. The 

 ganglionic layer forms a solid funnel-shaped mass of cells in the centre of the eye. 

 The inner reticular layer is well developed; the inner and outer nuclear layers are 

 merged into one. Rods are not found, cones are occasionally developed. The pig- 

 ment-layer is well developed. It entirely invests the eye, is free from pigment 

 over the distal face and variously pigmented over the sides and back. A small lens 

 was described, but this body is probably something else. It was so designated 

 because no other structure could be identified as a lens and because it was not known 

 what this structure was if not a lens. The pupil is frequently closed, and then the 

 iridian part of the eye is recognizable only by some elongated nuclei. 



III. BREEDING HABITS. 



The peculiar breeding habits of Amblyopsis have already been described by me 

 (Eigenmann, :00, p. 117). In contradiction to the then universally accepted view 

 that this fish brings forth living young, I showed that the female deposits her eggs, to 

 the number of about seventy, in her gill-cavity, where they are retained until the 

 yolk is practically all absorbed and the young fish has reached a length of 10 milli- 

 metres. All of the embryos and larvae described in the following pages were taken 

 from the gill-cavities of different females. The earliest date at which segmenting 



