ARTHROPODA. 317 



Arthropoda. 



616. Fixation of Ova, In most cases the ova of Arthropods 

 are fixed by heat in a more satisfactory way than by any other 

 means. This may be followed either by alcohol or some 

 watery hardening agent. If it be desired to avoid heating, 

 picro-sulphuric acid or liquid of Perenyi may be tried. 



Removal of Membranes. This is frequently very difficult, 

 and it may often be advisable not to attempt to remove them, 

 but to soften them with eau de Javelle or eau de Labarraque 

 (see the methods of Looss and LIST). 



MORGAN (Amer. Natural., xxii, 1888, p. 357; Zeit. /. wiss. 

 Mik., vi, 1, 1889, p. 69) recommends (for the ova of Peri- 

 planeta] eau de Labarraque diluted with five to eight volumes 

 of water, and slightly warmed. Thus used, it 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. 



617. HENKING'S Methods. For the whole subject of the 

 technique of the embryology of Insecta see an elaborate 

 paper by this specialist in Zeit. f. wiss. Mils., viii, 2, 1891, 

 p. 156. Henking agrees with other workers at this subject, 

 that in the majority of cases heat is the only available fixing 

 agent that will give fair results. He 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. 

 But, as might be expected, he finds that the preservation of 

 structures by this method is far from being perfectly satisfac- 

 tory, cell-contours being not at all sharply brought out by it, 

 and achromatic cell-structures being but imperfectly pre- 

 served. He finds that in some cases ova may be fixed with 

 liquid of Flemming, which, as may be supposed, gives incom- 

 parably better results in these respects. Suitable ova may 

 be put into liquid of Flemming (Henking does not say which 

 formula) for half an hour, then for two hours into the same 

 diluted with three volumes of water, then treated with alcohol 

 as usual. Boveri's picro-acetic acid was found not to pene- 

 trate the membranes. 



Henking thinks that eau de Javelle for softening mem- 



