460 THE ZOOLOGIST. 
and the head is provided with long slender antenne. The man- 
dibles are long and curved. The three abdominal appendages 
present under the microscope some interesting features. The 
larva of a Cleon has three tail-filaments. The middle filament 
bears on each side a number of very fine hairs. The two outer 
filaments have only hair on the left side, bearing on the right 
side the ‘‘ thorn ’’-like structure referred to above. The organs 
of respiration approach closely to gills in higher animals in the 
form of leaf-like plates ranged on each side of the body. ‘These, 
when the living larva is viewed under the microscope, move up 
and down with great rapidity, causing a constant stream of water 
to flow inwards. ; 
Mayfly larve, unlike many other aquatic larve, never come 
to the surface to breathe, but obtain all their oxygen directly - 
from the water. The larva grows but slowly, some taking two 
years to complete their metamorphosis. 
The pupa is active and resembles the larva, and traces of 
rudimentary wings only distinguish it from the latter. 
EXPLANATION OF ILLUSTRATION (p. 459). 
I. Portion of wing of Hphemera vulgata, showing ‘“‘squares”’ and 
“thorn” structure. | 
II. Tail-filament of a Cleon larva, showing hairs and ‘thorn ’”’- 
like structure. 
III. Portion of tail-filament of fly of Hphemera vulgata, showing 
divisions covered with minute hairs. 
~ TY. Gill of Clon larva. 
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