384 GEORGE H. CARPENTER AND MADEL 0. MACDOWELL. 
The tendon is articulated with the jaw at the boss ( b .). It is 
somewhat obliquely set as shown in figs. 13,15. 
The abductor muscle is much smaller than the adductor, 
and is completely covered by the fibres of the latter. It has 
two heads, and is inserted by means of a flat, rather spade- 
shaped tendon (fig. 14, td. 1 ) on the external corner of the 
mandible. 
Maxillulse and Hypopharynx. (PI. 36, figs. 20-22.) 
The hypopharynx lies between and somewhat behind the 
mandibles, and dorsal to the labium. In contrast to the 
•labrum it is quite symmetrical. 
It consists of a flexible chitinous plate, supported and 
strengthened by lateral and terminal complicated sclerites, 
and bearing two stout median teeth on its ventral aspect. 
The shape of the sclerites was very conveniently studied from 
a cast cuticle as well as from the organ dissected out of spirit- 
specimens of the larva. 
The lateral sclerite (U. scl.) is a long curved structure 
ending in a pointed apex (a.), sending out a toothed pro- 
jection (b.) ventrally, which passes forwards and inwards, 
and produced posteriorly into a long limb terminating in a 
delicately chitinised, foot ( pe .). This foot is provided with 
curved ridges, which serve for the attachment of muscles, 
and is strikingly comparable to a similar sclerite found at 
the back of the tongue in many Collembola (see Folsom [*99], 
pi. ii, fig. 10 ,pd.). Dorsally the lateral sclerite gives off another 
arm (c.), beset with sensory hairs and passing in towards 
the posterior median tooth (£."). (See PJ. 36, figs. 20, 21, 22.) 
Anteriorly the apex of the lateral sclerite articulates with 
a horizontal bar-like sclerite ( t . scl.), which meets and fuses 
with its companion of the other side. The cuticle is greatly 
thickened over the point of fusion to form the anterior median 
tooth (t/). 
The anterior portion of the hypopharynx is formed of a 
delicate cuticle beset with spines, which folds over towards 
