MACERATION METHODS FOR MOLLUSCA. 357 



has only been able to make the depigmentation process suc- 

 ceed with Helix pomatia ; with Prosobranchiata he failed. 



710. Eyes of Cephalopoda and Heteropoda (GEENACHEE, Abh. 

 naturf. Ges. Halle-a.-S., Bd. xvi ; Zeit. f. wiss. Mik., 1885, 

 p. 244). Fix in picro-sulphuric acid, or in a saturated solu- 

 tion of corrosive sublimate in picro-sulphuric acid (this mix- 

 ture is especially useful for Octopus, Eledone, and Sepia, but 

 does not succeed with the pelagic forms, such as Loligo, 

 Ommatostrephes, and Rossia) . Depigment the specimens with 

 hydrochloric acid (in preference to the nitric acid used by 

 Grenacher in former researches). The mixture 550 may also 

 be used. The operation of depigmentation may be combined 

 with that of staining ; if you stain with borax-carmine and 

 wash out in the last-mentioned mixture, the pigment will be 

 found to be removed quicker than the stain is washed out. 

 But this process is delicate, and requires a practised hand. 

 The operation of depigmentation may be carried out on sec- 

 tions, but it is better to use portions of retina of 2 to 5 mm. 

 in thickness. Grenacher mounted his preparations in castor 

 oil, see 393. 



Similar methods are recommended by the same author for 

 the eyes of Heteropoda (see Abh. naturf. Ges. Halle-a.-S. 

 1886 ; Zeit.f. iviss Mik., 1886, p. 243). 



711. Eyes of Chitonidse (MOSELEY, Quart. Journ. Mic. Sci. 

 1885, p. 40). Moseley worked by decalcifying the shell and 

 making sections. He places fragments of shell (of which the 

 tissues have previously been hardened in strong alcohol) in 

 100 to 200 c.c. of distilled water, and adds drop by drop con- 

 centrated nitric acid until gas is freely given off, which gene- 

 rally happens when from 3 to 4 per cent, of acid have been 

 added. If the decalcification is not complete at the end of 

 twelve hours, the objects should be removed to fresh distilled 

 water, and the operation repeated. This process is said to 

 give better results than the various processes of slow decal- 

 cification. 



711 a. Eyes of Pecten and other Forms (see PATTEN, in 

 Mitth. zool. Stat. Neapel, vi, 4, 1886, p. 733). 



712. Maceration Methods for Mollusca. For the study of 



