EMBKYOLOCHCAL METHODS. 309 



KOSTANECKI and WIER,/K.T>KI (Arcli. inik. Aunt., xlvii, 1896, 

 ]). 313) tix the spawn of Pliysa fontiiialis either in 1 1 to 2 

 per cent, nitric acid, or in " sublimate and 3 per cent, nitric 

 acid in the proportion of 2 : I" and bring tli rough suc- 

 cessive alcohols. They imbed entire ova in paraffin, but 

 isolated embryos in celloidin. 



/ 



622. CHITON, see MBTCALP, Stud, ttinl. Lab. Johns Hopkins Univ., v, 

 1893, p. 251. (Ova with young- embryos put for 20 to 45 seconds into 

 eau de Labarraque, then into water, in which the chorion swells and can 

 easily be removed.) 



623. Lam3llibran3hiata. - STAUFFACHEK (Jena Zeit., xxviii, 

 1893, p. 196) fixes embryos of Cyclax in sublimate, stains 

 with hseunalurn, and cuts in paraffin. 



LILLIE (Jt.uru. of Morpli., x, 1895, p. 7) fixes ova of Unio 

 for ten to twenty minutes in liquid of Perenyi, and preserves 

 them in 70 per cent, alcohol, or advanced embryos with liquid 

 of Merkel or sublimate, larvae with OG5 to (H per cent, 

 osmic acid, preserving them in glycerin. Glochidia may be 

 cut with the shell in paraffin of 58 melting-point ; they may 

 be anaesthetised with chloral hydrate before fixing. 



Aithropoda. 



624. Fixation of Ova. In many cases the ova of Arthropods 

 are best fixed by heat ( 13). This may be followed either 

 by alcohol or some watery hardening agent. If it be desired 

 to avoid heating, picro-nitric acid may be tried. 



625. Removal of Membranes. It may often be advisable not 

 to attempt to remove them, but to soften them with eau, de 

 Javelle or eau de Labarraque (see 553). 



MORGAN (Amer. Natural., xxii, 1888, p. 357) recommends 

 (for the ova of Periplttneta) eau de Labarraque diluted with 

 five to eight volumes of water, and slightly warmed. This 

 will soften the chitin membranes sufficiently in thirty to sixty 

 minutes, if employed before fixing. Fixed ova take longer. 

 The fluid must, of course, not be allowed to penetrate into 

 the interior of the ovum. 



626. HENKING'S Methods (Ze.it. /.<?. Mil-., viii, 1891, p. 

 ]56).--HENKiNG generally kills ova by plunging them into 

 hot water, or by pouring hot water on to them in a watch- 

 glass, and then removing into 70 per cent, alcohol. 



