UMBIIYOLOGICAL METHODS. 307 



Mollusca. 



620. Cephalopoda (Ussow, Arch, du li-iol., ii, 188], p. 582).- 

 Segmenting ova are placed in 2 per cent, solution of chromic 

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

 little acetic acid (one 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 cling to it, it may be removed by 

 pouring away the water and adding more. 



WATASE (Journ. of Morphol. } iv, 1891, p. 249) kills the ova 

 in the macerating mixture of the Hertwigs ( 534), 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 (Ann. Sc. Nat., vi, 18S7, p. 168) brings 

 ovarian ova of Sepia into a freshly prepared mixture of 

 picro-snlphuric 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 osmic 

 acid. 



KOKSCHELT (Festschrift Leu chart, 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. 



FAUSSKK (Mitth. ZooL Stat. Neapd, xiv, 1900, p. 83) 

 recommends picro-nitric acid. Fix in this, harden in alcohol, 

 bring the ova, still in their albumen, into hamialum, stain for 

 24 hours, wash in 1 per cent, alum solution for 24 hours, 

 when the albumen will be found softened so that the ova 

 can easily be extracted. 



621. 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 



