690 Pomona Coi,i.ege Journal of Entomology 



soil surrounding tlie pool. About two wet-ks' 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 alight- 

 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, whicli 

 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 

 distincth' 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 ratlur 

 close together, though not crowded. 



On each side of the venter of each segment, except the flrst 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 tlic 

 spiracular processes of the mosquito larva?, 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 tiie latter closes over it. 

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

 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 r.itlier dorsad 

 there is a smaller projection directed forward and outw.ird. which ))rotcets 

 another pair of spiracles. 



These, too, are telescoped, but in a difi'erent manner from tiie posterior ones; 

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

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

 otiiers that are functional, so that their .ability to swim on, in, or even under tlie 

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

 under tlie binocular micro.scope 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 tliough it is learned that the spiracles 

 may be drawn under cover. 



