THE FUNCTION OF REISSNER’S FIBER 139 
side tanks were glass fronted, and the only available glass- 
fronted tank, of a size to be readily transported, held but a 
comparatively small quantity of water and there were no facili- 
ties for connecting this tank with the aerating apparatus. A 
prolonged sojourn of the fish in this tank was not possible so 
that attempts to photograph under these conditions involved 
disturbing the specimens, transferring them in a bucket to the 
small tank and then waiting for them not only to settle down. but 
to settle in a position in which it would be possible to photo- 
graph them. One or two lucky snapshots were obtained but 
the method was, in general, a failure. 
An attempt to photograph the fish in their proper tanks in the 
laboratory encountered other difficulties. Of these the chief 
was connected with the light. With subdued daylight a com- 
paratively long exposure was needed and it was found in practice 
that the head region was always blurred by the respiratory 
movements even if the fish did not elect to move bodily during 
the process. 
In the end flash-light photographs were taken. The camera 
was fixed up opposite the tank in which was the specimen of 
which a photograph was desired and by the hght of an incan- 
descent gas lamp it was focussed upon a part of the tank a 
little within the glass front. Above the camera was stretched 
a piece of string upon which were placed a number of bent strips 
of magnesium ribbon. Usually some twenty inches of the ribbon 
were required, divided into four or more pieces. The gas lamp 
was then extinguished, and the aerating tube and bulb removed 
from the tank to do away with movement in the water. As 
soon as the specimen settled in a suitable position the strips of 
magnesium were lit, as nearly as possible, simultaneously. 
The reflection from the glass front of the tank was considerable, 
but in some of the later photographs this was diminished by 
igniting other strips of magnesium suspended immediately 
above the tank, care being taken to shield the lens from the 
direct rays from this source of illumination. Most of the 
photographs reproduced here were taken in this way. 
