SYRPHIDAE OF MAINS. 235 



appendages are rather prominent, longer than in a young larva of S. 

 americanus, and light in color like the rest of the body. Their tips are, 

 at first, rather remote from each other though with subsequent growth 

 and their greater elevation above the general body surface they become 

 contiguous. The two longitudinal fat bodies are discernible as a white 

 line on each side of the dorsal blood-vessel which is more prominent 

 in the posterior half of the body. The skin is faintly wrinkled trans- 

 versely. 



From this condition there seems to be a gradual growth until the 

 larva, when full-grown has reached a length of about 8 mm., width 

 2 mm., height 1.25 mm. It may then be described as follows: Shape 

 elongate oval, but much more pointed at the anterior end when extended 

 The outline is somewhat irregular due to folding and wrinkling of the 

 skin. The posterior end is rounding, truncate except for the projections 

 of the posterior breathing organ; (Fig. 31-66). 



Color green, with two longitudinal white stripes. This color is due to 

 colored visceral bodies which showHhrough the transparent skin. Along 

 the mid-dorsal line for two-thirds the length can be seen the narrow, 

 dark, pulsating blood-vessel. It is irregularly limited at .the sides by a 

 narrow mass of greenish, fatty globules changing gradually to whitish. 

 This whitish adipose matter forms the two prominent longitudinal white 

 stripes, .2 or .3 mm. wide and extending to within a few millimeters of 

 either end where they become much attenuated. The rest of the body, 

 except the appendages is green, darker on the sides. The breathing 

 tubes are light brown, black at the tips where the spiracles are located. 



The skin is finely papillose when magnified, bare except for the seg- 

 mental bristles which are light in color, not elongate and not conspicu- 

 ous. The outer pair of mouth-hooks (Fig. 31-67, c) is present. The 

 posterior respiratory appendage is prominent, elongate, about .5 mm. in 

 length, .33 to .4 mm. in breadth and a little less than .2 mm. in height ; 

 the two fused tubes diverging slightly at the extreme tip (Fig. 31-66, c ; 

 68). The median spiracle .08 to .09 mm. long, about .015 mm. broad, 

 the carina bearing the spiracle about three times as long as broad. The 

 circular plates about .05 mm. in diameter, their inner margins about .08 

 mm. apart. There is a short, but distinct, spur-like nodule on each 

 interspiracular space, which is continued down the side of the tube as 

 a more or less evident ridge. 



Puparium (Fig. 31-69, 70). Dimensions, average of eight: Length 

 about 5.25 mm., maximum breadth 2.5 mm., maximum height 2.3 mm. 

 This neglects the breathing tubes at the posterior end of the body 

 which may project .5 mm. farther posteriorly or be directed more dor- 

 sally. 



The puparium is broadest and deepest in front of the middle, the 

 anterior end bulbous ; strongly and evenly depressed and compressed to 

 the posterior end, the posterior elevation very gradual. (See Fig. 31-69 

 and 70). 



