278 
Nachdruck verboten. 
The Power of Resistance of Helophilus Larvae to Killing-Fluids. 
By E. V. Witcox, Ph. D., Cambrigde, Mass. U. 8, A. 
While studying at the Marine Laboratory of Mr. A. Acassız in 
Newport, R. I., during the summer of 1894, I found large numbers of 
the larvae of Helophilus. The larvae lived above high tide mark in 
small stagnant salt pools in excavations of the rocks. In these pools 
were decaying fish and lobsters which had been thrown away by the 
fishermen. 
As I was collecting material for spermatogenetic studies in insects 
I took some of them to fix and preserve. The larvae are small (about 
15 mm long exclusive of the tail, and 2 mm in diameter) and, appar- 
ently, delicate creatures. They are so translucent that the form and 
movements of the main organs can easily be seen through the integu- 
ment. It seemed, therefore, best to kill them in toto. I soon found, 
however, that none of the killing-fluids at my disposal, when used 
cold, would kill them, except after so long an exposure that the 
natural histological condition was quite destroyed. 
The first fluid tried was a saturated aqueous solution of corrosive 
sublimate. In this reagent the larvae lived and moved about for 
20 hours. At the end of that time they seemed to be dead, and they 
were then washed and put into 70 °/, alcohol where they soon revived 
and exhibited bodily movements for one hour longer. In a saturated 
aqueous solution of picric acid the larvae lived 31/, hours. 
In Hermann’s fluid 41/, hours. 
», vom RatnH’s modification of Hermann’s fluid 4 3 
„ FLEMMINng’s fluid 4 i 
„ strong formalin 1/,. hour. 
» 1 % osmic acid 4 hours. 
„ absolute alcohol Zr 
„ 90 %, alcohol 31), H 
„ pure glacial acetic acid 1'' howe 
„ oil of white thyme 8 minutes. 
„ Origanum oil 8 we 
» Clove oil 8 és 
» cedar oil 8 „4 
