No. 465.] STUDIES OF MYXINOIDS. 649 
interesting by experiment to see what use was made of them. 
The eyes are not exposed on the surface, like those of other 
fishes, but are covered by the skin, which is, however, trans- 
lucent for an area of about a square centimeter over them. 
There is nothing, therefore, to prevent the free passage of light. 
It has already been stated that when in the tank they would lie 
sometimes with their heads hidden in the rocks, but just as often 
with them projecting out into the light. It was suggested to 
me that this might be due to their wanting open water to 
breathe, and that possibly, other things being equal, they would 
prefer the dark. So to test it, two fish were placed in a large 
pan, three feet long by a foot wide, and half of the pan was 
covered making it very dark, while the other half was left open. 
It was a gray day, which made the light in the open end of the 
pan what they were accustomed to down in the tank. Both the 
fish were sluggish and did not swim much, but they were dis- 
turbed a number of times, and made to change positions. Each 
time when they settled down they seemed regardless of the 
light. They would settle quite as often at the light end of the 
pan as at the dark end. To make a surer test, two lively young 
fish were placed in a round dish about a foot in diameter and 
covered with an inch of water.. After swimming rapidly for a 
few minutes, they settled down into tight coils. The dish was 
placed on the table in the photographic dark room, and a micro- 
scope lamp was lighted. The lamp had a light-tight iron chim- 
ney, with a curved glass rod coming out opposite the flame to 
concentrate the light on the disc at its far end. This disc was 
about a centimeter in diameter. The fish chosen were particu- 
larly valuable for the experiment because they were young and 
the skin over the eyes was unusually clear. In one of them it 
was transparent, so that I could distinctly see the eye beneath 
it. In the dark room the circle of light coming from the glass 
disc was held an inch above the water. It could as well have 
been at the other end of the room as far as observable results 
were concerned, for they paid no attention to it. It was moved 
closer and closer to them, finally being placed under the surface 
of the water, and within an eighth of an inch of their skin, 
without obtaining an observable reaction. At all of these differ- 
