SMITH: EYES OF PULMOXATE GASTEROPODS. 239 



for the objects to come in contact with the acid below. Sections which 

 had been affixed to a slide in the ordinary way were transferred from weak 

 alcohol to water. Then, while the sections were still wet, the slide was 

 lowered into the test-tube until it rested on the upper ends of the two- 

 inch slides, and the tube was at once stoppered with a plug of cotton. 

 By heating the acid a little, chlorine gas was quickly generated, with 

 the result that the pigment was decolored more or less, depending upon 

 the amount of gas and the time during which it was permitted to act. 

 If the gas is allowed to act too long, the cytoplasm is reduced to a 

 structureless mass, but if the action is less prolonged the cytoplasm 

 still resembles to some extent that in sections not so treated. After 

 depigmentation the sections were transferred to water, in which they 

 remained until all of the decolorizer was removed, whereupon they were 

 stained. As it was the purpose of the decoloration to give a view of 

 that part of the sensory cell which passes through the pigment zone, the 

 sections were merely stained in eosin or acid fuchsine. The latter was 

 the more useful stain, because it seems to have the stronger affinity for 

 the cell boundaries. 



All attempts to get a methylen-blue impregnation of the retina by 

 injecting the stain into the body were fruitless. But if the eye-bearing 

 tentacles are cut off and placed for an hour or tw-o in a 2 per cent 

 solution of methylen blue in distilled water, the non-pigmented cells of 

 the retina become stained. I employed the ordinary "cold" method, 

 viz., fixing in Bethe's fluid for invertebrates, washing in distilled water or 

 salt solution, passing through grades of alcohol, and transferring to cedar 

 oil or xylol. Sections were afterward made. If the staining is not too 

 prolonged, none of the pigment cells of the retina will be affected. Since 

 the eye-capsule is the last part of the tentacle to be penetrated, the other 

 tissues of the tentacle are heavily overstained. Good preparations of 

 the sensory cells of the surface epithelium, it may be remarked, are also 

 to be obtained by the same method. 



For the differentiation of neurofibrillae three methods were used with 

 success. Apathy's after-gilding method was tried, but, although it is a 

 very good general stain for the retina, I have not been able to make it 

 differentiate the fibrils well. Since Bethe's method employs the same 

 fixation, prolonged effort to succeed with gold chloride was not made. 



In using the Bethe method I followed the modification introduced by 

 Prentiss (:03). The tissues were fixed in a saturated aqueous solution 

 of corrosive sublimate for six to twelve hours, and then passed through 

 grades of alcohol up to 70 per cent, iu which the sublimate was removed 



