438 RICHARD EVANS. 



prevented the paraffin sticking to the glass in the centre, while 

 near the margin, where there was no glycerine, it became firmly 

 adherent. 



The larvae, after they were placed in the watch-glasses, used 

 to swim about for a time, as a rule, near the surface, though a 

 few were always found to sink immediately and to move about 

 at the bottom. Those which sank, whether sooner or later, 

 usually became fixed and underwent metamorphosis. Some 

 larvse, however, never went to the bottom, but continued to 

 swim near the surface, and would fix ultimately to the film of 

 air at the surface of the water if allowed to do so. In order 

 that some use might be made of the larvae which fixed at the 

 surface, glass cover-slips were floated on the surface that they 

 might settle on them instead of fixing to the film of air. The 

 majority, however, fixed at the bottom of the watch-glasses. 

 After a certain number of larvse had become fixed, the watch- 

 glasses were sunk in a larger vessel, so that those undergoing 

 metamorphosis might have a greater supply of water, which 

 was always obtained direct from the river. 



Various reagents were used for the preservation of both 

 the free-swimming larvse and the fixed stages. The former 

 were merely dropped into the preserving fluid with a 

 pipette. The specimens which had fixed to the glass cover- 

 slips were similarly treated by dropping the cover-slip with 

 the individual fixed on it into the preserving medium. In no 

 case were these specimens removed from the cover-slips. 

 Those specimens which had fixed to the paraffin were removed 

 from the watch-glass together with a piece of the paraffin to 

 which they had become fixed by running a needle round them. 

 The piece of paraffin along with the specimen settled on it 

 floated to the surface, and was then dropped into the preserving 

 fluid in the same way as the cover-slips to which some larvae 

 had become fixed. 



The reagents used for preservation were the following : 



(a) Absolute Alcohol. — The specimens were placed in 

 absolute alcohol for five minutes, and were then removed into 

 90 per cent, alcohol. They were afterwards stained with a 



