EYES OF ARTHROPODS. 441 



sionally agitated, in order to prevent the acid from floating 

 on the chloroform. The reaction is complete in twenty-four 

 hours. 



Employed in this manner, nitric acid has no injurious 

 action on tissues. 



825. Eyes of Arthropods. LANKESTER and BOURNE (Quart. 

 Journ. Mic. Sci., 1883, p. 180) prepared the eyes of Limulus 

 as follows : Alcohol, turpentine,, paraffin; sections made and 

 carefully depigmented under the microscope with nitric acid 

 of 5 to 10 per cent., then mounted in balsam, some after 

 staining with borax-carmine, others unstained. Non-depig- 

 mented sections also mounted in the same manner. 



HICKSON (ibid., 1885, p. 243) prepared the eye of a fly as 

 follows : Remove the posterior wall of the head, and expose 

 the rest, with the eyes in situ, for twenty minutes to vapour 

 of osmium. Wash for a few minutes in 60 per cent, alcohol. 

 Harden in absolute alcohol. Make sections. To depigment 

 them, mount them on a slide with Mayer's albumen, remove 

 the paraffin with turpentine, treat them with absolute alcohol, 

 and invert the slide over a capsule containing 90 per cent, 

 alcohol to which a few drops of strong nitric acid have been 

 added. Nitrous vapours are freely given off, and the pigment 

 dissolves. The reaction may be stopped at any moment by 

 washing with pure alcohol. 



For dissociation preparations, put the eye or the optic 

 nerve for twenty-four hours into 5 per cent, solution of chloral 

 hydrate, tease, and mount in glycerin. If the elements of the 

 teased tissues be fixed to the slide by means of Mayer's 

 albumen, they may be washed with alcohol and stained in situ, 

 or they may be depigmented before staining. 



The methods of PARKER for eyes of scorpions have been 

 given, 579. 



For the eye of Homarus he gives the following staining 

 method (Bull. Mus. Comp. Zool., Cambridge, U.S.A., xx, 1890, 

 p. 1; Zeit. f. wiss. Mik., viii, 1, p. 82). Paraffin sections 

 fixed to slide with Schallibaum's collodion, and passed 

 through alcohol into water, are treated for half a minute with 

 0*1 per cent, caustic potash solution, well washed with water, 

 and stained for about three hours in Weigert's haematoxylin 

 solution at a temperature of 50 C. ; washed in water, de- 



