42 
tions of total disuse or total darkness, which would necessitate total dis- 
use. This view is upheld by the conditions found in Typhlogobius, as 
Ritter’s drawings and my own preparations show. In Typhlogobius the 
eye is functional in the young and remains a light-perceiving organ 
throughout life. The fish live under rocks between tide water (Higenmann 
90). We have here an eye in a condition of partial use, and the lens is not 
affected. The retina has, on the other hand, been horizontally reduced 
much more than in the Amblyopsidae, so that should the lens disappear, 
and Ritter found one specimen in which it was gone, the type of eye found 
in Troglichthys would be reached without passing through a stage found 
in Amblyopsis; it would be simply a horizontal contracting of the retina, 
not a collapsing of the entire eye. 
The question may with propriety be asked here, Do the most degen- 
erate eyes approach the condition of the pineal eye? It must be answered 
negatively. 
ONTOGENIC DEGENERATION. 
The developmental side of this question will be taken up with the de- 
velopment of the eye in Amblyopsis. 
The simplification of the eye in cornutus has been mentioned in the 
foregoing paragraphs. It may be recalled that the nuclear layers are 
thinner in the old than in the young. There is here not so much an elim- 
ination or destruction of element as a simplification of the arrangements 
of parts, comparatively few being present to start with. 
The steps in ontogenic degeneration can not be given with any degree 
of finality for Amblyopsis on account of the great variability of the eye 
in the adult. While the eyes of the very old have unquestionably degen- 
erated, there is no means of determining what the exact condition of a 
given eye was at its prime. In the largest individual examined the eye 
was on one side a mere jumble of scarcely distinguishable cells, the pig- 
ment cells and scleral cartilages being the only things that would permit 
its recognition as an eye. On the other side the degree of development 
was better. The scleral cartilages are not affected by the degenerative 
processes and are the only structures that are not so affected. The fact 
that the eyes are undergoing ontogenic degeneration may be taken, as 
suggested by Kohl, that these eyes have not yet reached a condition of 
