EMBRYOLOGY 385 



acid for two minutes, and then in distilled water, to which a 

 little acetic acid (1 drop to a watch-glassful) has been added, for 

 two minutes. If an incision be now made into the egg-membrane, 

 the yolk flows away and the blastoderm remains ; if any yolk 

 still clings to it, it may be removed by pouring away the water 

 and adding more. 



Watase (Journ. of Morph., iv, 1891, p. 249) kills the ova in 

 the macerating mixture of the Hertwigs (§ 568), and as soon as 

 the blastoderm turns white and opaque removes it under dilute 

 glycerin. Treatment with liquid of Perenyi is recommended for 

 surface views. 



ViALLETON (Ami. Sc. Ncit., vi, 1887, p. 168) brings ovarian ova 

 of Sepia into a freshly prepared mixture of picro-sulphuric acid 

 and 2 per cent, solution of bichromate of potash in equal parts, 

 and after one or two minutes incises them in the equator, fixes 

 for an hour and a half in picro-sulphuric acid the halves that 

 contain the formative vitellus, separates this from the nutritive 

 vitellus with a spatula, spreads it out, and hardens it in alcohol of 

 70 to 90 per cent. He fixes entire ova in liquid of Flemming or 

 osmie acid. 



KoRSCHELT {Festschrift Leuckart, Leipzig, 1892, p. 348) fixes 

 advanced embryos of Loligo in liquid of Flemming, sublimate, 

 picro-sulphuric acid, or 0-2 per cent, chromic acid. This last is 

 specially good for young embryos if it is washed out with many 

 changes of picric acid. 



Faussek (Mitth. Zool. Stat. Neapel, xiv, 1900, p. 83) recom- 

 mends picro-nitrie acid. Fix in this, harden in alcohol, bring 

 the ova, still in their albumen, into haemalum, stain for twenty- 

 four hours, wash in 1 per cent, alum solution for t\venty-four 

 hours, when the albumen will be found softened so that the ova 

 can easily be extracted. 



843. Gastropoda (Henneguy). Ova of Helix may be fixed for 

 from four to six hours in Mayer's picro-nitric acid. The carbonate 

 of lime that encrusts the external membrane is thus dissolved, 

 and the albuminous coat of the egg is coagulated. The egg is 

 opened with needles, the albumen comes away in bits, and the 

 embryo can be removed. 



Henchman {Bull. Mits. Comp. Zool., Harvard, xx, 1890, p. 171) 

 fixes ova of Limax with 0-33 per cent, chromic acid, or with 

 liquid of Perenyi. It is best to remove only the outer envelope 

 before putting into the chromic acid, the inner membrane being 

 removed after two or three minutes therein. Where Perenyi is 

 used the membranes must be removed first, as the albumen will 

 else coagulate in such a way as to prevent the removal of the 

 embryos. 



Meisenheimer {Zeit. wiss. Zool., Ixii, 1896, p. 417)- dissects 

 out the embryos of Limax and fixes them with picro-sulphuric 



VADE-MECUM. JS 



