228 THE SCOTTISH NATURALIST 



With regard to sections, of course the tissues must be 

 " fixed," and many insects because of their chitinous and 

 hairy investment must be cut in order to allow the fluid 

 to penetrate. But for teaching and other purposes it is 

 sometimes desired to make transverse and longitudinal 

 sections of an entire insect. With this object in view, it is 

 best, if one is at liberty to choose, to select an insect which 

 is as free as possible from hairs. The following method 

 gave perfectly satisfactory results with Ephemerid larvae 

 and nymphs : 



Lift each specimen from the water in which it has been living, 

 and touch it for a moment with blotting paper or a cloth to 

 dry it slightly. 

 Drop it alive into Carnoy's fluid, which kills it instantly, and 



leave for four hours. 

 Transfer to absolute alcohol for a day or two, changing the 

 alcohol several times until all trace of the acetic acid has 

 disappeared. 

 Transfer to cedar oil and leave till clear. 



After this take it through the paraffin process in the usual way, 

 using 5 2 paraffin, and cedar oil as a solvent, because it 

 causes less brittleness than chloroform or xylol. With 

 the Cambridge "rocker" the sections should be cut about 

 5 n (8 teeth). 

 Any of the customary staining methods may be used. 



I like Carnoy's fixative because it kills instantaneously, 

 is very penetrating, and, according to my experience, causes 

 no shrinkage. 1 For embryological work I have lately used 

 Bles's fluid with perfect satisfaction (alcohol JO per cent., 90 

 parts ; formalin, 7 parts ; glacial acetic acid, 3 parts). Some 

 skilled workers have recently advocated the use of strong 

 formalin (Schering's solution) especially for killing larvae. 

 When I tried it for Chironomus larvae it ruptured the blood 

 gills ; but the method deserves attention. As every entomol- 

 ogist knows, dropping into boiling water is one of the best 

 as well as the most humane means of killing larvae for 

 ordinary purposes, but 1 doubt if by this means the various 

 tissues would be fixed in a way suitable for histological 

 study. 



1 If allowed to act too long, Carnoy's fluid will cause swelling. 



