ON SALT WATER INSECTS. 47 



"I send you the larva aucl pupa of a dipterous insect [Ephydra], 

 found in the salt brine at the salt works near Equality, Gallatin Co., 

 111., in such prodigious quantities as to fill up the wooden conduit 

 pipes. These larvas [puparia] are gregarious, collecting in masses, 

 and form great rope-like bunches by clinging around small fibrous 

 roots on the sides of the little ditch that conveys the brine from the 

 first "Graduation or Thorn house," to the pump at the furnace. The 

 brine as it comes from the well has a strength equal to 7 3-10 Baume, 

 and is gi'aduated after the German plan, by showering it successively 

 over thorn bushes arranged on beams from top to bottom of three sepa- 

 rate frames, from forty to forty-five feet high, called "Graduation or 

 Thorn houses." What is remarkable in this is, that the above larvae 

 can nowhere be found except in the brine after first graduation, that 

 is, passed over the first house, when they are found in such quantities 

 as to prove a great nuisance. Neither in the fresh water, weak brine, 

 or brine of second and third graduation can they be found at all. 

 The people at the works believe that they are genex-ated by some 

 peculiar property in the water acquired after first graduation. I send 

 them in their favorite brine." 



The pupa of another species of fly (Eristalis ?) was found in the same 

 place. " The fly [identifled by Baron Osten-Sacken as a species of 

 Ephydra] of the first worm sent you was seen in great abundance on 

 the pool at the bottom of the Graduation house. When alarmed they 

 will fly up a few inches from the water, then alight upon it again in 

 another place, and will glide about upon its surface with rapidity and 

 the greatest ease. I think the worms come from a small egg, de- 

 posited by the fly, which sinks to the bottom of the water, where it is 

 hatched, and the first visible stage of life is a very small white mag- 

 got, that crawls, or rather wriggles about on the bottom until the 

 pupa is matured ; they then attach themselves by a thread-like 

 appendage to sticks and roots and to one another, forming great 

 knots or ropes. In this way they remain flxed until the fly is fledged. 

 I send you some of the small white maggots. You have already some 

 of the matured larvae, and empty cases." 



The specimens of the larvae sent by Mr. Cox in the 

 brine were too much decayed for identification, so that at 

 present we can only describe the puparium and imago. 

 The body of the puparium (Fig. 5, 5) is rather long, 

 cylindrical, but flattened towards the thorax and head, 

 with the tip so recurved that the anal, or last pair 

 of abdominal feet, curve inwards touching the abdomen 

 under the sixth pair of feet. From the tergum of the last 

 segment is thrown off a long breathing tube, terminating 

 in two widely diverging, slender, filiform branches. The 

 head is not more corneous than the remaining part of the 

 body, and is continuous with the thorax, being trans- 

 versely flattened, oblong, and half as long as broad. The 

 mouth-parts and eyes are obsolete. The thorax is much 



