ANATOMY AND PHYSIOLOGY ej 
fat-tissues. The corpuscles (leucocytes, or phagocytes) which 
in some insects absorb effete larval tissues during meta- 
morphosis have been by some authors regarded as wandering 
fat-cells. Cells constituting the pericardial fat-body are at- 
tached to the lateral muscles (alary muscles) of the dorsal 
vessel, but almost nothing is known as 
Fic. 166. 
to their function. Associated with the 
fat-body proper are the peculiar cells 
known as a@nocytes. These occur in 
most insects, in segmentally-arranged 
clusters on each side of the abdomen, 
and consist of exceptionally large cells, 
more or less round or oval (Fig. 166), 
each with a large round, oval or elon- 
gate nucleus. These peculiar cells are 
usually separate from one another, but (Enocyitemantkaatons 
are held in clusters by tracheal branches. Tee ee ce 
Their function is unknown. Finally, the 
fat-body is the basis of the luminosity, or so-called phospho- 
rescence, of insects. 
Luminosity.—This phenomenon appears sporadically and 
by various means in protozoans, worms, insects, fishes and 
other animals. Luminosity in insects, though sometimes 
merely an incidental and pathological effect of bacteria, is usu- 
ally produced by special organs in which light is generated 
probably by the oxidation of a fatty substance. 
There are not many luminous insects. Those best known 
are the Mexican and West Indian beetles of the genus Py- 
rophorus (Elateridz), in which the pronotum bears a pair of 
luminous spots, and the common fire-flies (Lampyride). In 
Lampyridz, the light is emitted from the ventral side of the 
posterior abdominal segments. In our common Photinus, the 
seat of the light is a modified portion of the fat-body—a 
photogenic plate, situated immediately under the integument 
and supplied with a profusion of fine tracheal branches. The 
cells of the photogenic plate, it is said, secrete a substance which 
