ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 599 



between two cover-glasses, and when these have been drawn apart each 

 is hehl over a gas or spirit-lamp flame until the layer of nerve-matter 

 becomes of a blackish-brown coloiu', and a distinct smell of burning is 

 perceived. The preparation is then mounted in xylol balsam or 

 dammar. 



In such preparations the nerve-cells and glia nuclei are seen to be 

 of a dark-brown colour ; the blood-vessels and their nuclei are also 

 distinctly visible. The glia cells form a delicate reticulum, which 

 connects the nerve-tubules with the blood-vessels and with the nerve- 

 cells. 



In order to ascertain if the reticulum was produced by a coagulation 

 of the medullary substance, the fresh layer was soaked in ether for 

 ten minutes, and the cover-glass then heated. It was found that the 

 same reticulum appeared, but the cover-glass layer required to be 

 treated for a longer time. It was afterwards found that if the cover- 

 glasses were not separated for about one hour the preparations were 

 more effective. 



(2) Double cover-glass preparations. — A j)iece of grey substance 

 about the size of a hemp-seed is pressed between two cover-glasses, 

 between which are placed thin strips of tissue paper. The two cover- 

 glasses, still sticking together, are then immersed in picrocarmine or in 

 an aqueous solution of methylen-blue. The preparations required fifteen 

 days to become perfectly stained. They are then dehydi-ated in 

 absolute alcohol (foui* days), cleared up in oil of cloves, then placed for 

 two days in xylol, and finally fixed to a slide by pouring some xylol 

 dammar over them. When the dammar has di-ied the surface is 

 cleaned. 



Simple Method of freeing Frogs' Ova.* — Prof. F. Blochmann has 

 discovered a simple method of freeing the ova of frogs from the 

 gelatinous matter which surrounds them and from their envelope. A 

 number of young eggs are preserved in chrom-osmic-acetic a.cid and 

 then well washed in water. They are then placed in a shallow glass 

 with a quantity of eau de Javelle diluted with three or four times its 

 volume of water ; from time to time the glass is shaken. In from a 

 quarter to half an hour the eggs are quite free. The fluid must then be 

 carefully drawn off, the eggs washed with water, and concentrated 

 alcohol be gradually applied ; the eggs should be kept in the dark, so 

 as to remove the remains of the chromic acid. Eggs thus treated, and 

 then stained with borax-carmine and cut into sections, show no signs of 

 any injury. Prof. Blochmann believes that it will be possible to improve 

 this method, which he commends to embryologists. 



Investigation of Ova of Caprella ferox.f— Madlle. (Dr.) S. Pereya- 

 slawzewa found, like M. Mayer, that the chorion covering the egg of 

 CaprellidaB offers very great difficulties to the observer ; like M. Mayer, 

 she was tempted to renounce her word. Instead thereof, however, she 

 devised a plan for detaching the compact chorion. The eggs are jilaced 

 in a watch-glass with only sufficient water to keep them moist ; boilin^ 

 water is poured on them, and the chorion can then be removed with 

 needles. The ova are then placed for from three to five hours in weak 

 spirit, and then in absolute alcohol for twelve hom-s. Eggs prepared in 



* Zool. Anzeig., xii. (1889) pp. 269-70. 



t Bull. Soc. Imp. Nat. Moscou, 1888 (1889) pp. 582-^ 



2 T 2 



