Eyes of Molluscs and Arthropods. 737 



eitlier weak chromic. or siilplmric acid. For the outer ganglionic cclls, 

 wbieli are very difficult to isolate, niaecration in V.-.oVo chromic acid 

 gave excellent results, after previously fixing the tissue iu ^4^0 foi* a 

 few miuutes. 



For the retinophorae, \^oVo chromic acid for 4 or 5 days proved 

 very iiseful. 



Treatment with sulphuric acid , 5 drops to 30 graras of sea water, ga ve 

 the very best results for the nerve endings in the retinophorae, — not iu 

 the r ods — and for the nervous, inner prolongations of the outer gang- 

 lionic cells. It was only by prolunged maceration, twenty days or more, 

 that the inner ganglionic cells could be separated from the retinophorae. 



Iu Order to isolate pieces of the cornea with the subjacent pseudo- 

 cornea and the circular fibres on the outer surface of the lens, it is 

 better to macerate the eyes in sulphuric acid. In the sanie way, the 

 lens, which, by this treatment, retains to perfection its natural shape, 

 may be dissected out and studied to advantage. 



It is necessary for the study of the circular retinal membrane, the 

 septum, and the retina itself, to isolate the latter intact. Maceration iu 

 chromic acid either makes the retina too brittle, or too inconsisteut, 

 while the nerve fibres of the axial nerve brauch remain so firmly 

 attached to the retina that it is difficult to isolate it without injury. But 

 this may be easily and suceessfully done by maceration, for 1 or 2 days, 

 in a weak solution of sulphuric acid. By this treatment, the retina, to- 

 gether with the septum and circular retinal membrane, remains in- 

 tact, while its connections with the Avall of the eye are so weakened that 

 there is little difficulty in detaching the retina entire. 



The color of the red pigment layer is destroyed by all reagents 

 except sublimate: but after it is once fixed in this manner, it is not 

 altered by any subsequent treatment. 



In Pecten Jacohaeus^ it is only possible to isolate the retinophorae 

 by maceration: by treating with bot chromic acid, their rods may be 

 isolated without the cells. 



By macerating the small eyes oi Pecten opercularis in rather strong 

 sulphuric acid , the entire retinophorae together with the rods may be 

 isolated, giving very instructive preparations. 



The peripheral, outer ganglionic cells may be seen by macerating 

 the eyes for 24 or 48 hours in sulphuric acid, and then studying the 

 outer surface of the isolated retina. 



The argentea may be very easily separated in large sheets, by 

 macerating for 4 or 5 days in bichromate of potash. 



Mittheilangen a. d. Zoolog. Station zu Neapel. Bd. VI. 49 



