LUMBRICUS. 321 



626. Amphipoda (Orchestia] (ULIANIN, Zeit.f. wiss. Zool., xxxv, 1881, 

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

 with picro-sulphuric acid (Kleinenberg's formula). This causes the chorion 

 to swell and burst. Ova in later stages, in which the embryo is surrounded 

 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 picro-sulphuric acid. 



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

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



Vermes. 



628. Tsenia (v. BENEPEN, 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. 



629. Planaria (!IJIMA, Zeit. f. wins. 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. 



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

 p. 207). Fix with Kleinenberg's picro-sulphuric acid, or, 

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

 through successive alcohols, stain with Kleinenberg's hsenia- 

 toxylin, and cut in paraffin. 



WILSON (Journ. of Morph., iii, 1889, p. 445 ; Journ. Roy. 

 Mic. Soc., 1890, p. 402) finds that liquid of Perenyi is by far 

 the best fixing reagent, being in most respects superior even 

 to Flemming's. Fix for fifteen to sixty minutes, wash out in 

 70 per cent, alcohol, stain with borax-carmine, wash out in 

 acid alcohol, treat for a few minutes with ammoniacal alcohol 

 to neutralise the acid, and after-stain for twelve hours with 



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