690 Pomona College Journal of Entomology 



soil surrounding the pool. About two weeks' time is required between pupatio: 

 and the emergence of the adult. 



The adult fly is small and black and conspicuous. It always remains near 

 the petroleum pools, flying about and over them when disturbed, and soon aliglit- 

 ing again on the margin or on some projecting stone or stick within the pool. In 

 this respect it is not at all different from the other flies of this family, which 

 seem to frequent the larval habitat closely. 



An examination of the larva externally shows that it is not strikingly 

 abnormal in any way, except for the terminal spiracles, and even these are mor 

 or less similar to other related maggots. The body consists of twelve segments 

 distinctly marked, is elongate-ovate in form, roundly acute at the anterior end 

 and less so posteriorly, with four processes at the posterior end projecting back- 

 wards. The body is rather transparent, showing the alimentary canal easily to 

 the naked eye. It is covered entirely with minute chitinous, spine-like processes, 

 of the same color as the body surface, more or less variable in length and rather 

 close together, though not crowded. 



On each side of the venter of each segment, except the first two, there is a 

 knob-like projection and two large ones on the dorsum of the next to last seg- 

 ment. The anal segment is produced inferiorly into two long knob-like projec- 

 tions, as in many other maggots, and superiorly into two similar projections, 

 directed upward and backward, with the tips of each heavily chitinized and black. 

 Near the tip of the heavily chitinized portion are four fan-like groups of cilia 

 projecting out horizontally. These serve the same purpose as the flaps on the 

 spiracular processes of the mosquito larvae, that is, keeping the tip of the process 

 which bears the stigmata above the oil surface. The posterior segment which 

 bears these processes is retractile into the pre-anal segment. When the larva 

 goes under the surface the caudal segment is drawn forward and upward in a 

 somwhat rotating fashion into the pre-anal segment and the latter closes over it. 

 In this way the spiracular processes are entirely covered and protected from tlu- 

 oil. A maggot with its spiracles "telescoped" gives the appearance of being 

 broadly rounded posteriorly with two black spots (the black tips of the spiracles) 

 near the end. 



At each side of the second segment near the front margin and rather dorsad 

 there is a smaller projection directed forward and outward, which protects 

 another pair of spiracles. 



These, too, are telescoped, but in a different manner from the posterior ones ; 

 these are simply drawn straight in, truly telescoped, while the posterior pair are 

 drawn forward into a definite cavity. Beside these four spiracles there are no 

 others that are functional, so that their ability to swim on, in, or even under the 

 petroleum is easily understood. It is very interesting, indeed, to watch them 

 under the binocular microscope go through the contortions of telescoping their 

 exposed organs. That they should exist as long as they must have done in coming 

 to my laboratory is very remarkable, even though it is learned that the sjairacles 

 may be drawn under cover. 



