EYES OF CEPHALOPODA AND HETEROPODA. 437 



the animal be thrown into osmic acid or Miiller's solution, if I understand 

 the writer justly, no secretion of mucus will occur. 



815. Eyes of Gastropoda (FLEMMING, Arcli.f. mik. Anat., 1870, 

 p. 441). The first difficulty here is to obtain the excision of 

 an exserted eye. It is impossible to sever the exserted 

 peduncle in a living animal without ite retracting at least 

 partially before the cut is completed. Never mind that ; make 

 a rapid cut at the base, and throw the organ into very dilute 

 chromic acid, or 4 per cent, bichromate ; after a short time 

 it will evaginate, and remain as completely erect as if alive. 

 Harden in 1 per cent, osmium, in alcohol, or in bichromate. 



CARRIERE (Zool. Anz., 1886, p. 221) gives the following in- 

 structions : Remove the eye, together with a portion of the 

 tentacle, and fix it by exposing it for some minutes to vapour 

 of osmium. Make sections according to the usual methods, 

 and fix them on a slide with Schallibaum's collodion. Stain 

 them with picro-carmine ; or first depigment them by very 

 careful treatment with very dilute eau de Javelle, and then 

 stain with picro-carmine. Mount in dammar. Successful 

 preparations show the tissues perfectly preserved ; but Car- 

 riere has only been able to make the depigmentation process 

 succeed with Helix pomatia ; with Prosobranchiata he failed. 



816^ Eyes of Cephalopoda and Heteropoda (GRENACHER, 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 583 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. 

 Bub 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 425. 



