THE WESTERN GRASS-STEM SAWTLY. 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: 

 • j.1,1 . • j 1-11 l i_ ii Newly-hatched larva. Greatly 



pointed, the points chisel-shaped, beveled enlarged 

 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 



