26 THE AMERICAN MONTHLY [February, 



rounded and dark colored at the free end and movable. This is the 

 eye, mounted upon a stalk controlled by muscles so as to be movable 

 in a variety of directions. If you leave the cray-fish "• to his own de- 

 vices" vou will see that he moves the eye about to suit his own con- 

 venience. After killing in chloroform (see vol. viii, p. 82), remove 

 both eyes with a scalpel by cutting carefully at the joint between the 

 eye and the body. In doing this do not pull or tear anything, as it 

 might injure the parts within the stalk ; cut straight across them with 

 sharp scalpel or fine sharp scizzors. One unused to cells can hardly re- 

 alize their extreme delicacy and how little crushing, tearing and push- 

 ing they can stand. Preserve the eyes, after removal, in some hard- 

 ening reagent. The reagent can reach the tissue within the stalk by 

 the opening at the base. Any of many methods may be used. Here 

 are two actual records, either of which imitated perfectly will give a 

 fair result. (My sections of the eye, not being the result of special ex- 

 periments, are by no means ideally perfect. They are, however, as 

 good as or better than a beginner can expect to make, and will there- 

 fore be better for this purpose than sections which he could not expect 

 to imitate.) 



First Method. — Immerse the eye in 1% chromic acid 5 days, then in 

 50% alcohol one hour, then in 70% one day, then in absolute alcohol or ■ 

 stain, and then imbed in paraffin by the usual method. 



Second Method. — The rods shown in figure 4 were drawn from a 

 section prepared by first method in 18S4. When I began this series of 

 articles in 1SS6, I prepared an eye in a different manner and with bet- 

 ter success so far as regards some features. Its exact history was as 

 follows : 



(1) Saturated watery solution of corrosive sublimate, 45 min. (2) 

 Running water, 75 min. (3) 50% alcohol, 30 min. (4) 70% alcohol, 

 27 hours. (5) Picronitric acid, full strength, 6o\ hours. (6) 70% al- 

 cohol, 11 days z\ hours. (7) Kleinenberg's hematoxylin, 2 clays. 

 (8) Washed in 70% alcohol, 10 min. (9) Absolute alcohol, iy 1 ^ days. 

 (10) Chloroform, 21 hours. (11) Chloroform and paraffin solution, 

 5 T V hours. (12) Pure paraffin at 56 C, 1 hour. (13) Blocked for 

 section cutting. (14) Sliced in microtome longitudinally. (15) Sec- 

 tions cemented to slide with collodion and oil of cloves'. (16) Warmed 

 gently over lamp and washed with turpentine. (17) Turpentine wiped 

 away and replaced by chloroform balsam and covered. 



For the sake of any who have begun using this periodical since the 

 beginning of this series of articles, brief comment may be added upon 

 the different steps of this somewhat complicated process, showing the 

 reasons for some of them. 



The purpose of the second method was chiefly to secure good prep- 

 arations of the parts in the lower part of the stalk of the eye. The 

 corrosive sublimate was used for them and to reach the terminal por- 

 tion if possible. This latter it accomplished, but poorly in places, though 

 it did succeed here and there. The running water is to remove the cor- 

 rosive so that it will not crystallize in the cells. When alcohol is used it is 

 followed at once by dilute and this by strong alcohol. The water and 

 weak alcohol should not be continued longer than here practised, but 

 the specimen once in 70% alcohol can remain there for any time longer 

 than 24 hours. Picronitric acid (made by adding 2 parts strong nitric 



