360 SOME ZOOLOGICAL METHODS. 



may stain before imbedding, with alum-carmine or picro- 

 carmine (five to six days). I should say Mayer's tincture of 

 cochineal would generally be preferable. 



The same methods are applicable to the preparation of the 

 ova of Insecta, for instance Periplaneta (see MORGAN, Am. Hon. 

 Mic. Journ., ix, 1888, p. 234). 



716. Other Depigmentation Methods. Besides the depig- 

 mentation processes discussed in Chap. XXIV, the following 

 methods are available. 



SAZEPIN'S Method for Eyes of Chilognatha (Mem. Acad. Imp. 

 St. Petersb., xxxii, 9, 1884, pp. 11, 12). Sazepin treats 

 antennae that have been dehydrated with alcohol by steeping 

 them in chloroform. The reaction is slow, the chitin becomes 

 gradually less opaque, but the pigment does not entirely dis- 

 appear. In order to remove the last trace of it, it will be 

 sufficient if a drop of fuming nitric acid be now added to the 

 chloroform. The mixture must be occasionally 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. 



717. 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 the 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 GO 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. Tin- reaction may be stopped at any moment by 

 wasliinr with pure alcohol. 



