279 
In strong potassic hydrate 10 minutes. 
„ Eau de Javelle 3 hours. 
„ benzole 4 minutes. 
29 xylol 4 99 
» pure HNO, year 
„ pure HCl 6 i. 
» pure H,SO, 10 seconds. 
In the above list the time given in each case is the length of 
time during which the larvae showed bodily movements while sub- 
merged in the particular fluid. In all cases the larvae were entirely 
submerged with the exception of the end of the tail, which the animal 
held at the surface of the fluid. As is well known, these larvae breath 
through the tail, and, therefore, they are enabled to obtain air freely 
while their bodies are exposed to the action of the killing-fluid. Thus 
we have a much better test of the penetrating power of reagents than 
we could have in the case of larvae which are entirely submerged in 
the fluid. For in the latter case death may result partly from a lack 
of air, which the Helophilus larvae could breath just as freely in a 
killing-fluid as in their salt pools. 
The larvae were quickly killed by the standard fluids, if a slit 
had previously been cut in the integument. When the larvae were 
first placed in Eau de Javelle, or a weak solution of potassic hydrate 
for 5—10 minutes, the killing fluids required only a few minutes to 
penetrate the integument. 
Hot killing-fluids, or hot water, killed the larvae instantly, but 
hot FLemmine’s fluid, hot corrosive sublimate etc. did not fix the 
larvae. These fluids were, therefore, no better than hot water. And 
I used hot water by preference. Then by slitting the bodies open and 
hardening in alcohol (beginning with 30°/,) they were well preserved. 
Since the above was written I have received a letter from Dr. 
S. W. WILLIsToN, to whom I had sent some of the larvae for identi- 
fication. He says: — “They in all probability belong with either Helo- 
philus, Eristalis, or Mallota..... I have never known of their occur- 
ring in salt water.” 
In Osten-Sacken’s essay “On the so-called Bugonia of the 
Ancients and its Relations to Eristalis tenax, Bull. della Soc. Ent. 
Ital. 1893, he says: — “civilization offers it (E. tenax), its drains, 
canalizations, cess-pools and dung-heaps in which it can wallow” etc. 
OsTEN-SACKEN mentions his having seen adult E. tenax in Newport, 
R. L, in 1877. | 
