THE WESTERN GRASS-STEM SAWFLY. 11 
not yet visible. Over night, at the close of the fifth day, the jaws 
turn brown and the eye spots appear and darken. Usually, after 
the fourth day, the muscular system of the larva is in almost con- 
stant motion, shifting and adjusting, with the heart pulsating and 
the muscles moving, all clearly to be seen through the transparent 
membrane that serves as the shell. 
The activity of the larva within the sac increases during the sixth 
day, and either on this day or the seventh it escapes from its confine- 
ment by a series of convulsive movements that rupture the delicate 
shell and set it free. 
After the first day the egg changes shape, becomes intumescent, 
generally loses its crescentic shape entirely, and grows oval or reni- 
form in outline. 
THE LARVA 
When it escapes from the egg the larva 'fig. 6) possesses a very large 
head armed with a pair of powerful biting jaws, a weak, slender body, 
and a most vigorous appetite. It is very 
active from the start and begins almost at 
once to feed upon the living parenchymatous 
tissue by which it is surrounded in the inte- 
rior of the stem, excavating for itself a 
threadlike gallery both above and below the 
spot where the egg formerly lay. The larva 
is at first nearly transparent and colorless 
until it becomes filled with the tissue on 
which it exists. 
The body segments are strongly and clearly 
marked from the time the larva leaves the 
egg. The jaWS are brown, three Or four Fig. 6.— Western grass-stem sawfly: 
pointed, the points chisel-shaped, beveled enterjed^ e ^ a ' ° reat 7 
on the inside edge. The brown face plate 
is filled with crossed bands of striated muscular fiber that actuate the 
powerful jaws which form the most important item of the domestic 
economy of the young Cephus. The caudal horn, by means of which 
the larva moves up and down in its gallery, is also brown and is 
armed, even in the first instar, with a series of stout bristles at the 
base of its cylindrical and squarely truncate extremity. The larva 
is footless, the position of the legs being marked by minute, rounded 
tubercles terminating in a few short bristles. 
Although the primary excavation made by the larva may extend 
for a short distance above the egg cell, the general course of the 
progress is invariably downward. In its earlier stages of existence, 
at least, the larva traverses its gallery several times, swallowing 
repeatedly the same fragments of tissue that have already been 
devoured during the first excavation of the stem. Young larvae are 
