Sept., 1917-] Marchand: Notes on Early Stages of Chrysops. 157 



The tracheae are dark or shining silvery-white, according" to the 

 light, and are filled with air. The two main stems converge towards 

 the end of the body, where they terminate in a sharp acuminate tail 

 (fig. 8). 



Description Summarized. — Body spindle-shaped, 12-segmented, 

 slightly above i mm. in length; general color grayish white, semi- 

 transparent. Head retractile; mouth parts small, dark brownish, 

 chitinized; eyes situated on pharynx, black. Last segment ending in 

 an acuminate tail, on the base of which are two bristles on each side. 

 Segments 4-10 with two pairs of ventral and two pairs of lateral 

 prolegs; the latter armed with short stiff bristles pointing backward 

 (Plate XI, fig. 5). Intestine straight, except in the middle region of 

 the body. Main tracheal trunks parallel in the posterior half of the 

 body, while in the anterior half forming two large semicircular loops, 

 ending in the region of the fourth segment, and here dividing up into 

 small tracheae. Chitinous surface striated as seen in Plate XI. figs. 

 4 and 5, Graber's organ consisting of a capsule containing only one 

 pair of black pedunculate bodies. 



Movements of the Larva. — These are carried out in the following 

 way : the larva presses the prolegs against the surface on which it 

 moves, then drives the main mass of the body through them by means 

 of contractions in the posterior half of the body, while the intestine 

 ■is protruded forwards and the head exserted. Then the prolegs 

 abandon their attachment, and seem to be moved forward by the 

 elasticity of the body to which they are attached. 



Activities of the Larvae. — The larvae were kept in small dishes with 

 water and some aquatic plants. In water without special care they 

 perished in less than a week; when fed and taken care of, they lived 

 slightly longer. As food, crushed dragonfly larvae, mosquito larvae, 

 crushed small caterpillars were given and accepted. However, their 

 numbers always rapidly diminished. This is partly accounted for by 

 their cannibalistic tendencies. Mitzmain states that larvae of Tabanus 

 striahis, even if other food was offered, preferred their own kind to 

 any other food given. Another difficulty was to keep the water in 

 small jars free from putrefaction. For this purpose green plants 

 {Elodea, MyriophyUnm) were given, but these plants decayed, and 

 the larvae perished. Mud seems necessary for the larvae to burrow 

 into, but renders their observation impossible. With a proper method. 



