274 EMBRYOLOGICAL METHODS. 



bryo from the yolk by means of a sharp knife, and stain with picro-carmine 

 and mount in balsam. 



592. Amphipoda (Orchestia) (ULIANIN, Zeit.f. wiss. Zool., xxxv, 1881, 

 p. 441). Ova in the earliest stages of development were treated for two 

 hours with picrosulphuric acid (Kleinenberg's formula). This causes the 

 chorioii to swell and burst. Wash out with alcohol, stain with Beale's car- 

 mine. Make sections. Ova in later stages, in which the embryo is sur- 

 rounded by a cuticular membrane, which encloses an albuminous liquid, 

 must have this membrane torn with needles and the albuminous liquid 

 allowed to ooze out before placing in the picrosulphuric acid. 



593. Maturation of Ova, and other early stages. These should be 

 studied by the methods given in the chapter on Cytological Methods. 



Vermes. 



594. Taenia (v. BENEDEN, Arch, de Biol., ii, 1881, p. 187). 

 Ova in which a chitinous membrane has formed around the 

 embryo are impervious to reagents. They may be put on a 

 slide with a drop of some liquid and covered. Then, by with- 

 drawing the liquid by means of blotting-paper, the cover may 

 be made to gradually press on them so as to burst the mem- 

 branes, and the embryo may then be treated with the usual 

 reagents. 



595. Planaria (!IJIMA, Zeit.f. wiss. Zool, xl, 1884, p. 359). 

 The capsule containing the ova (of fresh-water Planaria) 

 is opened with needles on a slide, in a drop of 2 per cent, 

 nitric acid. The ova are extracted and covered (the cover 

 being supported by paper, or by wax feet). After half an 

 hour they are treated with successive alcohols under the cover, 

 and finally mounted in glycerin. For sections, the whole of 

 the contents of a capsule is hardened in the mass in 1 per 

 cent, chromic acid and cut together. 



596. Lumbricus (KLEINENBERG, Quart. Journ. Mic. Sci., 1879, 

 p. 207). Fix with Kleinenberg's picrosulphuric acid, or, 

 which is not quite so good, with vapours of osmium, pass 

 through successive alcohols, stain with Klrinenberg'.s 

 toxylin, and cut in paraffin. 



597. Ascaris. See the chapter on Cytological Methods. 



