360 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
are unknown, while in some other instances, the females alone are 
known. A number of observations of the relations between size of 
eyes, length and complexity of antennae, and the development of 
the photogenic function in the sexes have been made, the extreme 
of which appears to be reached in forms like Phengodes laticollis, 
where the male is winged, has very large eyes, large, plumose 
antennae and is non-luminous, while the female is intensely luminous 
from a large number of photogenic organs, is entirely apterous, has 
very small eyes, and only rudimentary antennae. 
The reported luminosity of midges (Chironomus) has long been a 
matter of curiosity and speculation. It has at last been proven by 
Issatschenko (?°)—as was previously suspected—that the light emis- 
sion in these insects is due to bacterial infection, apparently patho- 
genic. This strongly recalls Giard’s observation (?) of the patho- 
genic relation of a species of photogenic microorganism to Talitrus. 
It may also have a confirmatory value toward the explanation offered 
by Distant (#°) of the alleged luminosity of Fulgora. In view of the 
known propensity of owls to hide during the day in hollow trees, 
and the frequent infection of such trees by photogenic molds, etc., it 
seems that a similar explanation might be advanced for the occasional 
instances in which these birds have been reported to be luminous, 
such as those cited by Dobbs and Moffatt (1'), and Purdy (°*). 
A number of observers have, at various times, reported the lumi- 
-nosity of various species of earth-worms. Walter (*) attributes this 
property to the secretion of certain glands in the skin of the worm, 
which is of interest when considered with the studies of Galloway 
(72, 23) on the related marine Odontosyllids, and those of Kutschera 
(8) on Acholoe; in this latter instance the luminosity appears to have 
a defensive function. 
So far as marine forms in general are concerned, the photogenic 
function appears to have a variety of uses, its significance to a given 
organism depending on the method of life of the species. Alcock (') 
brings out this variation in the use of the function in marine organ- 
isms very well. Nutting (°°) has also had a very interesting paper 
on this phase of the subject. With the increasing knowledge of the 
existence of light-giving structures in numbers of species of fish, 
cephalopods, crustanceans, and many lower forms, the views as to 
the use of such organs to their possessors are gradually broadening, 
and the conception of the conditions of life in the depths of the sea 
becoming more and more definite and interesting. 
Several studies of the structure and development of the luminous 
organs in various fish have been made, perhaps the most interesting 
and complete of which are those of Greene (77) and Gatti (4); neither 
of these papers can be conveniently quoted here, but both are 
important. 
