282 EMBRYOLOGICAL METHODS. 



70 per cent, alcohol for twenty-four hours, and for the larvae picro- 

 nitric acid. 



616. Test-Cells of Ascidians (MORGAN, Journ. of Morphol, iv. 1890, 

 p. 195). Tease fresh ovaries in very weak osmic acid, wash in distilled 

 water, treat for half an hour with 1 per cent, silver nitrate, wash for 

 half an hour in 2 per cent, acetic acid and reduce in sunlight. Imbed 

 in paraffin. By this process the limits of the follicle cells are demon- 

 strated. 



617. Buds. PIZON (Ann. Sc. Nat., xix, 1893, p. 5) studies the 

 gemmation of the composite Ascidians either on entire corms, 

 which he first bleaches with peroxide of hydrogen and then stains, 

 or by making sections, after anaesthetising the colonies with cocain 

 of 1 : 1000, fixing in glacial acetic acid or pier o -sulphuric or liquid 

 of Flemming, and staining in toto with borax carmine or alum 

 carmine, or with a strong solution of methylen blue in alcohol of 

 90 or 100 per cent, (after BERNARD, ibid., ix, 1890, p. 97). 



RITTER (Journ. of Morph., xii, 1896, p. 150) recommends for 

 fixing Perophora and Goodsiria picro-sulphuric acid. 



Bryozoa. 



618. Statoblasts. BRAEM (Bibl. ZooL, Chun and Leuckart, 

 6 Heft, 1890, p. 95) fixes statoblasts of Cristatella with hot con- 

 centrated solution of sublimate for ten minutes, brings them into 

 water and there incises them with a razor, and after half an hour 

 passes them gradually into alcohol. He stains with picro-carmine. 



Mollusca. 



619. Cephalopoda (Ussow, Arch, de Biol., ii, 1881, p. 582). 

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

 for two minutes, and then in distilled w^ater, 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 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, 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, 



