322 ENTOMOLOGY. 



olive-oil, .and each section washed with a mixture of 4 parts of oil of 

 turpentine and 1 of creosote to dissolve the embedding substance sur- 

 rounding the section. Mount in Canada balsam. 



To preserve the embryo entire, the shell is to be removed as above 

 described, after coagulation. The egg is then placed in a drop of 

 water on the stage, and with a low power the embryo is extracted 

 from the vitellus. It is cleaned as much as possible, so that no por- 

 tion of the vitellus adheres to it, and mounted in glycerinated gela- 

 tine, previously colored with methyl-green. By this method the 

 embryo takes from the gelatine an excess of color, and is thus 

 stained after the preparation is made. If it is colored first and then 

 placed in colorless gelatine it will always lose color (sometimes com- 

 pletely) if the gelatine is only a little greater in volume than the em- 

 bryo. (Journ. de Microgr., vL (1882) pp. 220-1.) 



Surface Study of Eggs, and Hardening for Cutting, etc. Mr. W. 

 A. Locy* adopts, for studying the eggs of spiders while alive, the 

 long-used method of immersion in oil, which should be perfectly 

 clear and odorless. The external features can be studied to better 

 advantage by mounting the eggs in alcohol after they have been 

 freed from the chorion and stained. Another valuable method for 

 surface study consists in clearing the already stained egg in clove- 

 oil. The thickness of the blastoderm is most easily determined in 

 this way. 



The best method of hardening preparatory to sectioning is that of 

 heating the water to about 80 C., and then, after cooling slowly, 

 treating with the usual grades of alcohol. Good results are obtained 

 with Perenyi's fluid, which renders the yolk less brittle. Osmic 

 acid does not penetrate thechoriou, and chromic acid or acid alcohol 

 are not easily soaked out on account of the thickness of the choriou. 



Borax-carmine is, on the whole, the best staining fluid. It is 

 difficult to make the dye penetrate the chorion, and, after hatching, 

 the cuticula forms a similar obstacle. This difficulty may be over- 

 come by prolonged immersion in the staining fluid. In some cases 

 seventy-two hours were required to obtain a sufficient depth of color. 

 In order to avoid maceration, which would result from so long-con- 

 tinued immersion in a weak alcoholic dye, the staining process may 

 be interrupted at the end of every twenty-four hours by transferring 

 to 70 per cent alcohol for an hour or more. 



After most methods of hardening the yolk becomes very brittle, 

 and the sections crumble. This difficulty may be overcome by col- 

 lodionizing the cut surface before making each section, in the man- 

 ner described by Dr. Mark.f 



* Amer. Natural., xix. (1885), pp. 102-23. f Ibid., p. 628. 



