238 bulletin: museum of comparative zoology. 



To secure an eye of Limax or Helix I have usually simply snipped 

 off with scissors the extended tentacle behind the eye and placed the 

 piece in fixing fluid. As complete a penetration of the fixing fluids 

 seems to be secured in this way as by dissecting out the eye from the 

 tentacle, for it is the eye-capsule which offers the most serious difficulty 

 to the penetration of reagents. 



The rods were studied in the fresh condition by teasing the retina in 

 0.9 per cent salt solution. A more dilute solution produces swelling of 

 the rod. In teased preparations, small groups of cells, and especially 

 isolated rods, are abundant. Such preparations were further studied 

 under the polariscope after the method employed by Howard (:03). 

 Reference will be made to this method again. 



For a maceration fluid one volume of Flemming's weaker mixture was 

 added to nine volumes of water. This solution proved to be satisfac- 

 tory, for it seems to fix the tissues, and yet they may be torn apart 

 easily. The osmic acid guards against the growth of fungi, which one 

 cannot refrain from suspecting must have found their way into some of 

 Patten's preparations. The eye, having macerated for forty-eight hours 

 or more, was teased into several pieces in a drop of 10 per cent glycerine 

 on a long cover-glass. A square cover-glass with wax feet at the corners 

 was placed over the drop. 



By gentle, prolonged tapping on the square cover, the retinal cells 

 were more or less isolated and separated from the capsule. The cells, 

 or groups of cells, could now be studied either from above or below. As 

 the water evaporated from the glycerine, stronger grades of glycerine 

 were added. For convenience the largest possible eyes were chosen for 

 maceration. 



I agree with Hesse that Flemming's solution gives the best fixation 

 for ordinary sections. Both acetic-sublimate and Perenyi's fluid were 

 also used. The sections were stained either in brazilin or in Heiden- 

 hain's iron-haematoxylin, followed by orange-G. They were usually cut 

 6|/x in thickness, sometimes 3J/u.. 



To depigment the molluscan retina without also destroying the retinal 

 cells seems hitherto to have been possible for no one. The method 

 which I have employed is as follows :• — 



A few crystals of potassium chlorate were placed in a large test-tube 

 containing a little strong nitric acid. A few two-inch glass slides were 

 placed side by side in the bottom of the test-tube. Rising above the acid, 

 these slides not only formed a firm basis which would support any object 

 which might be introduced into the tube, but they also made it impossible 



