14 Psyche [March-June 
noted that as the time for emergence of the beetle approaches 
the glow usually becomes very faint although rarely persisting 
for a brief period after emergence. Degeneration extends still 
further in another related genus Ellychnia, and in our common 
E. corrusca no adult luminescence is to be noted, at least in 
completely matured individuals. The larval organs persist in a 
degenerating condition in adult beetles as was shown by Wil- 
liams. 2 Some recent workers do not recognize these several 
genera as distinct, grouping them all together as Lucidota which 
is the oldest name. 
The question as to whether the adult photogenic organ in 
these species should be regarded as vestigial or whether it rep- 
resents a stage preceding the development of the large and bril- 
liant organ of Photinus is of considerable interest. Inasmuch as 
luminescence in these beetles has been generally thought to be 
a sexual manifestation which facilitates mating, we should be 
inclined to consider the reduced condition in Lucidota as vesti- 
gial. On the other hand, the fact that the large adult organ in 
the male of Photinus is without question a structure developed 
later and in addition to the persisting larval organs which pass 
over into the adult without loss of function, we must conclude 
that the pair of larval organs are phylogenetically older and 
that the imaginal organ is a more recent acquisition. What pur- 
pose the larval organs may serve is not clear. It has been sug- 
gested that they may enable the larvae to recognize one another 
and it is known that these creatures are gregarious, although 
not to a high degree. We can hardly admit on this basis that 
luminous spots can play any real part in the ecology of the 
larval beetles. Aside from the complex morphology of the bril- 
liant imaginal organs, the integument covering them is greatly 
modified by the complete loss of pigment. In Lucidota there is 
no indication of any such change as the ventral abdominal seg- 
ments are fully blackened in conformity with the general very 
dark body color of the beetles, and the visibility of the persistent 
larval organs is effected only through the weakly pigmented, 
extrusible tip of the abdomen. 
It is unfortunate that we do not know more concerning these 
less spectacular fireflies and the place that they occupy in the 
evolution of this most varied and remarkable group of luminous 
beetles. 
2 Journ. Morphol., vol. 28, pp. 145-207 (1916). 
