CUTTING AND MOUNTING EGGS. 321 



staining with borax- or picro-carmine and bleu de Lyon are advised. 

 (Zeits. f. wiss. Zool., xliii., 1886, 537; Journ. Roy. Micr. Soc., 

 Oct. 1887, 841.) 



Herr J. Nusbaum thinks that one method of preservation can 

 never afford satisfactory material for study, as each method gives 

 different results. He treated fresh eggs with Kleinenberg's or 

 Perenyi's fluid, or treated them a few seconds with hot water and 

 then with bichromate of potash. The eggs in either case were 

 hardened in 70 per cent and then absolute alcohol ; then colored in 

 toto by haematoxylin, borax-carmine, or red magdala ; the latter gave 

 a perfect staining reagent, coloring the eggs and embryos in a few 

 hours, and very intensely, though sometimes very uniformly.* 



Preparing Embryos of Insects. In a paper on the embryonic 

 development of the Bombycidae, Dr. S. Selvatico describes the 

 methods he has made use of both for the preparation of entire em- 

 bryos and for sections. The species employed were Bombyx mori, 

 Attacus mylitta, and Saturnia, pyri. 



The eggs are first coagulated by plunging them in water at 75 C. 

 With a pair of fine-pointed forceps a small piece is removed from the 

 shell, in the case of Bombyx, without disturbing the underlying 

 parts. With a little care this is easily done, because on the eggs be- 

 coming cold, their contents are somewhat contracted and do not 

 touch the shell. In the case of Attacus and Saturnia the eggs have 

 a harder shell but are larger, and a razor was employed by the 

 author. 



They are then hardened by leaving them for twelve hours in a 

 .002 per cent solution of chromic acid, and for twelve hours more 

 in a .005 solution. Then with a little care the shell can be easily 

 removed by employing the forceps or cutting it round with a razor. 



The entire contents having been removed, the egg is freed from 

 chromic acid by leaving it in 30 per cent alcohol for a day, the 

 alcohol being renewed until it is no longer colored yellow. 



For staining, the egg is placed in picrocarmine for twenty-four 

 hours and washed in 30 per cent alcohol to remove the picric acid. 

 When it has been well washed it may be kept in 30 per cent alcohol 

 until sections are required. 



Previous to cutting sections the egg should be placed in absolute 

 alcohol for half an hour, and then for a few moments in essence of 

 bergamot. Dry and embed in a mixture of 4 parts of spermaceti 

 and 1 of cacao butter, to which is added, according to the tempera- 

 ture, some drops of castor-oil. The knife should be moistened with 



* Arch. Zool. Exper., 1887, 134; Journ. Roy. Micr. Soc., 1887, 

 21 



