June, 19 1 2.] Aldrich : Biology of Western Ephydra. 87 



the two segments preceding this one, but they have no regular arrange- 

 ment. The dorsum of the puparium is pigmented in a broad irregular vitta 

 almost the whole length, as in the larva. The anal tube has no basal forks 

 or filaments; the tube and its terminal forks are more uniform in length than 

 in the larval stage, being of a hard consistency. The segment which bears the 

 first prolegs has a flattened surface above, which continues to the anterior 

 end of the puparium ; this somewhat shield-shaped piece splits along the sides, 

 and many of the flies emerge from the crack without pushing off the entire 

 front end (Fig. 16, arrow) as is supposed to be characteristic of Diptera 

 cyclorhapha. The flat upper piece is readily removed, and is shown in Fig. 

 7. It bears at the sides the rudiments of two spiracles. The lower portion 

 of the anterior end also readily cracks off, just behind the first prolegs, and 

 is shown in Fig. 17; it contains the remains of the mouth-parts of the larva 

 — a flat black sclerite embedded in the integument, and the jaw-capsule 

 frame farther back, to the front edge of the latter being attached two long 

 curved hooks, which in the figure seem to connect it with the former, but 

 which really bend downward at their points. As the pupa forms it retracts 

 from the anterior end of the shell and leaves these larval organs outside. 



Larva (PI. IX, Fig. 13). — The fullgrown larva measures about 12 mm. in 

 length in alcoholic specimens; the length of the anal tube and its forks is 

 highly variable and depends entirely on the amount of retraction that has 

 taken place ; generally it is much shorter in preserved specimens than it is 

 observed to be in fresh material. The most prominent characteristic of this 

 species is the highly pigmented stripe down the back, almost as wide as the 

 larva, with irregular edges, narrower toward the front edge of each segment 

 and then gradually widening to the posterior border. This pigmentation 

 shows under the high power of the compound microscope as a covering of 

 minute spines, a sort of shagreen; but with moderate powers it simply appears 

 like a blackish pigment. The eight pairs of prolegs are conspicuous, as in 

 allied forms, the last pair being much the largest, with the hooks reversed in 

 position, enabling the insect to grasp a solid object between them and the 

 next pair anterior, or sometimes the second pair anterior. This is a very 

 characteristic feature of the species. The anal tube bears no filaments at 

 base, and the apical ones emerge directly from the open end of the tube, into 

 which they can be drawn so that only the tips are visible. The spiracles at 

 the end of the two forks appear to be non-functional, and as in gracilis the 

 organ serves as a tracheal gill. 



The part of the insect anterior to the segment bearing the first prolegs 

 is considered by Brauer to consist of five segments (Denksch. Kais. Ak. Wiss., 

 XLVII, 39, 1883), but of these only three can be discerned, the other two 

 being retracted in the anterior end. The second of the visible segments bears 

 on its under surface a large, transversely oblong black spot or sclerite : this 

 seems to be a hardened spot in the integument for the attachment of some of 

 the muscles of the jaw-capsule. There is no true head, the retracted part 

 being mainly the jaw mechanism. Two minute two-jointed antenna can 

 sometimes be detected.- but they are capable of retraction. The jaws are 



