REPTILES, BATRACHIANS, AND FISHES. 47 
near the eyes, where they are sometimes of a pinkish or greenish 
colour. These are the so-called phosphorescent organs ; and 
although their luminous properties are now generally admitted, 
it is desirable to obtain corroborative evidence as to their function 
from the living fishes, with special reference to the question whether 
the luminosity is subject to the will of the fish. 
Labelling of Specimens. 
It is most important that every specimen should bear an indication 
of the place, date, and circumstances under which it was collected, 
as well as the native name, if it can be ascertained. This is best 
done by keeping a notebook or diary, in which the entries are made, 
each entry bearing a number corresponding to a label attached to 
the specimen. Threaded parchment labels, a quarter of a square inch 
in size, are most suitable for the purpose, the numbers being inscribed 
beforehand in ink, which, when allowed to dry well, will not run. 
Pencil-marks are liable to become illegible through rubbing off. In 
the case of fishes a second label may be inserted under the left gill- 
cover, as a precaution in case the threaded label should become 
detached and lost. 
