smith: eyes of pulmonate gasteropods. 241 



distribution of the main mass of fibrils, it makes their study difficult; 

 their adequate illustration is impossible. 



The intra citam method of Prentiss (:03) rests upon the assumption 

 that, because the methylen blue has a selective affinity for the neuron, 

 ft must have a special affinity for just that part of the neuron which has 

 to do with the conduction of impulses. The impregnation was accom- 

 plished by the method already described. The librillae were differ- 

 entiated in a 0.9 per cent salt-solution for three or four hours at room 

 temperature, after which they were fixed in ice-cold ammonium molyb- 

 date and treated as in the ordinary " cold " method. This method is 

 not successful for the rods, but as these can be so easily studied by sim- 

 pler methods, the defect is not serious. A very useful addition to the 

 method of Prentiss was made by counterstaining the sections with 

 orange-G ; for there is the same need of it here as in the original method 

 of Bethe. The tissues were imbedded in paraffiue melting at GO C, 

 so that the sections wrinkled in cutting very little. After having been 

 attached to the slide with egg-albumen the sections were freed from 

 paraffiue in xylol at room temperature. The slides were next transferred 

 to ice-cold xylol for a few minutes, and then to ice-cold 100 per cent 

 alcohol, in which there was dissolved a little orange-G. Thus at the 

 same time water was extracted from the egg-albumen and a counter- 

 stain secured. The slides were then returned first to ice-cold, and then 

 to warmer, xylol. 



The Morphology of the Eye of Limax. 



The general structure of the eye of snails and its relations to the re- 

 mainder of the eye-stalk have been described repeatedly. The eye of 

 Limax maxim us, however, has never been adequately described, notwith- 

 standing the fact that it departs remarkably from the typical pulmonate 

 eye, and that it is particularly favorable for illustrating the minute struc- 

 ture of this type of eye. I shall therefore begin with a brief account of 

 the morphology of the eye, which will also facilitate an understanding of 

 the sensory cells. 



When the eye-stalk is cut off and dropped into a fixing solution, it 

 partly retracts. The eye is thus pulled down into the tentacle for some 

 distance. Flemming ('72, p. 3GG) found that, in a four per cent solu- 

 tion of potassium bichromate, the eye-stalk will relax in many cases so 

 as to bring the eye back to its original distal position. However, the 

 position which the eye has in the tentacle when fixed is unimportant, 

 since any good fixing reagent will penetrate the tentacle readily. Figure 

 vol. xlviii. — No. 3 1G 



