DEVELOPMENT OF PHRYGANIDS. 555 



found almost impossible to remove it again. Eggs of a species 

 of water-beetle — which I believe to be Hydrophilus — that were 

 preserved in this way have now been in strong alcohol (96 per 

 cent.) for six months, and they still have a very perceptible 

 yellow colour, due to the picric acid which still remains, and 

 makes it very diflBcult to stain them with hsematoxylin. A 

 number of experiments have also been made in the use of 

 corrosive sublimate, but with very unsatisfactory results ; the 

 eggs were rendered very brittle, and good staining, which is 

 the chief difficulty in the study of insect eggs, was made im- 

 possible. Insect eggs seem to have the power to withstand in 

 a great degree the penetration of staining fluids, which is 

 probably due to the compact tissues, rendered much more so 

 by the use of sublimate, since it causes a considerable shrink- 

 age. At all events, if the eggs are killed by a prolonged and 

 gentle heat, and then hardened in alcohol, no difficulty will be 

 found in staining them, and the histological characters are 

 preserved in as much perfection as by any other method at 

 present at our command. 



Bobretzky was the first to use heat in the preparation of 

 eggs for sectioning, but he used it principally as a means to 

 increase the penetration of the chromic acid, a reagent which 

 adds materially to the difficulty of staining them. 



The small size of the eggs made it impracticable to remove 

 the chorion, the presence of which proved a serious obstacle 

 to the penetration of staining fluids. Only alcoholic stains 

 would penetrate at all, and of these Kleinenberg^s haematoxylin 

 gave by far the best results. Partial and varied success was 

 obtained from saffanine dissolved in 90 per cent, alcohol, and 

 Grenacher's alcoholic borax carmine. Saff"ronine gave better 

 results than the carmine, since it never failed to stain, whereas 

 the latter did.^ 



For the early stages of the egg a light red stain like cochineal 



' Later experiments, with a 70 per cent, solution of cochineal, have 

 given very good results indeed ; and in cases where it is diflScult for the fluid 

 to penetrate, this stain produces the required result far better and more rapidly 

 than all others. 



