EMBRYOLOGY 387 



or sublimate, larvae with O-Oo to 0-1 per cent, osmic acid, pre- 

 serving 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. 



ARTHROPODA * 



846. Fixation of Ova. la many cases the ova of Arthropods 

 are best fixed by heat (§ 11). This may be followed either by 

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

 avoid heating, jiicro-nitric acid may be tried. 



Heavy yolked insect eggs are dealt with as follows by Miss E. H. 

 Slifer and R. L. King {Science, 1933), This is a modification of 

 A. Petrunkewitsch's cupric-phenol method, and is used by Miss 

 Slifer and R. King especially for grasshopper (locust) eggs. 



Fix in Carnoy-Lebrun. Wash in iodised alcohol, cut in half 

 and store the micropyle halves in 75 per cent, alcohol. When 

 needed, expose for twenty-four hours to 4 per cent, phenol in 

 80 per cent, alcohol, dehydrate in 95 per cent, alcohol, clear in 

 carbol-xylol, infiltrate with paraffin, each one blocked with the 

 cut end outwards. Trim until the yolk is just exposed and soak 

 in water for twenty-four to forty-eight hours. This eliminates 

 the necessity of moistening each section separately. 



Another method is to fix in Bouin overnight. Transfer to the 

 phenol-alcohol solution mentioned above for twenty-four hours. 

 Imbed and section. Good for chromosomes. 



847. 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 § 586. 



Morgan {Amer. Natural., xxii, 1888, p. 357) recommends (for 

 the ova of Periplaneta) eau de Labarraque diluted with 5 to 8 

 volumes of water, and slightly warmed. This will soften the 

 chitin membranes sufficiently in thirty to sixty minutes, if em- 

 ployed before fixing. Fixed ova take longer. The fluid must, of 

 course, not be allowed to penetrate into the interior of the ovum. 



848. Henking's Methods [Zeit. wiss. Mik., viii, 1891, p. 156). 

 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. 



He thinks that eau de Javelle for softening membranes is best 

 avoided. They should either be dissected away or left in situ, 

 and cut with the rest of the egg, according to the nature of the 

 case. To avoid brittleness of the yolk proceed as follows : After . 

 fixing and treating with alcohol, prick the chorion and stain with 

 borax-carmine. Put the stained ova for twelve hours into a 

 mixture containing 20 c.c. of 70 per cent, alcohol, 1 drop of 



* See remarks in §§ 1 182 et seq. 



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