360 ANNUAL EEPOET 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 {Cliironomus) has long been a 

 matter of curiosity and speculation. It has at last been proven by 

 Issatschenko ( 30 ) — 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 ( 25 ) 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 ( 10 ) 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 Moff att ( u ) , and Purdy ( 58a ) . 



A number of observers have, at various times, reported the lumi- 

 nosity of various species of earth-worms. Walter ( 69 ) 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 

 ( 22 > 23 ) on the related marine Odontosyllids, and those of Kutschera 

 ( 38 ) 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 ( 55 ) 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 ( 27 ) and Gatti ( 24 ) ; neither 

 of these papers can be conveniently quoted here, but both are 

 important. 



