
618 THE AMERICAN NATURALIST. | [Vor. XXXVI. 
Sisyra, there is an interpolated sclerite on the ventral side. 
The head has on the dorsal surface a pair of hairs directed 
forward, and on the ventral surface another pair similarly 
directed but much more elongate. 
The larval respiratory apparatus consists of external gills in 
the form of a pair of jointed appendages on the ventral surface of 
\ the first seven abdom- 
à y inal segments, folded 
| under the body so as 
to be unnoticeable in 
| a dorsal view. They 
| / are moved intermit- 
| | j tently ina rapid, 
| shuttle-like vibration. 
Westwood has figured 
them with five joints, 
but I have found them 
uniformly to have only 
three. The first pair 
seem to have lost the 
articulation between 
the first and second 
joints. These have 
thus become two- 
jointed appendages. 
Near the point of 
attachment the first 
pair have a curious 
hook-like projection 
(6, Fig. 5); directed 
inward toward the 
body. This appears on 
the second pair merely 
as a knob, and gradu- 
; ally decreases in prom- 
inence, until it disappears almost entirely on the sixth and 
seventh pair (a, Fig. 5). On each pair of appendages except 
the first, at its articulation with the second joint the first one 

Fic. 4. — Sisyra umbrata, larva. x 15. 
