CHAPTER XXV. 283 



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. 



KOESCHELT (Festchrift 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) recommends 

 picro-nitric acid. Fix in this, harden in alcohol, bring the ova, 

 still in their albumen, into heemalum, stain for twenty-four hours, 

 wash in 1 per cent, alum solution for twenty-four hours, when the 

 albumen will be found softened so that the ova can easily be 

 extracted. 



620. 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. Mus. 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 acid or 

 concentrated sublimate. Advanced embryos are first got into 

 extension by means of 2 per cent, cocaine, or are rapidly killed with 

 hot sublimate. 



SCHMIDT (Entw. Pulmonaten, Dorpat, 1891, p. 4) fixes the ova 

 in toto with concentrated sublimate, and dissects them out afterwards. 



Similarly KOFOID (Bull. Mus. Harvard Coll., xxvii, 1895, p. 35). Or, 

 preferably, the ova are put into salt solution, the shell removed, the 

 albumen removed with a pipette full of salt solution, which dissolves 

 it ; the ova are then fixed for one minute in Fol's modification of 

 liquid of Flemming, and brought direct into Orth's picro-lithum- 

 carmine. See also LINVILLE, ibid., 1900, p. 215, who adopts this 



