1889.] MICROSCOPICAL JOtJENAL. 27 



acid to 98 parts saturated watery picric acid solution) was used to de- 

 calcify the outer shell. In the first method, this decalcifying was done 

 by the chromic acid at the same time with the hardening. The result- 

 ant sections by the first method are not as good as those b}' the second, 

 except with regard to the crystalline cones. These are some of them 

 shown by the second method, but are badlv confused with other retinal 

 elements. The alcohol next used removed the picric acid from the 

 specimen and permitted the access of borax carmine, which stained beauti- 

 fully the ganglionic nerve cells and also demonstrated very clearly the 

 cells of the corneal hypodermis in many places. The remaining treat- 

 ment w^as theordinary treatment for imbedding and mounting and does not 

 require special comment. One who follows this method carefuHv will 

 have no difliculty in finding all the structures pointed out bv Professor 

 Huxlev in •' The Cray-fish " (page 119), and many more which he there 

 passes by without remark. A section prepared in this way and exam- 

 ined with the low powder is represented in figure 1 of the accompanying 

 plate. To its examination let us now proceed. It must be noticed that 

 since the eye is in reality hemi-spherical, not every longitudinal section 

 will give the appearance seen in figure i , but only the few wdiich pass 

 through the centre of the stalk or near it. Those which pass to one side 

 of the centre will of course cut diagonally through the radially disposed 

 parts, and such sections will be very much harder to interpret. I have 

 chosen the most favorable section for description. In securing such a 

 section, it will be necessary to mount every section when you think you 

 are near the centre of the stalk, and examine each one until you reach 

 the one passing in the plane of a radius. Several successive sections will 

 now be good, and then the remainder of the eye will be of little use. 



2. Minute Anatomy with the low power. — Since the entire sec- 

 tion cannot be seen at once with a ^-inch objective it will be well first to 

 examine it with a hand lens or with an inch or lower objective to identify 

 its chief parts, and then place these under a ^-inch objective for low power 

 study. You will at once observe (i) the semi-circular cornea bounded 

 by a band which suddenly on the side becomes thicker, and bounds the 

 stalk as the ordinary eptdertnis or C7iticlc (cu) ; (2) the area w'ithin 

 the cornea occupied by rod-shaped bodies which radiate toward the 

 cornea from the central part of the semi-circular area and form collec- 

 tively the retina or terminal portion of the optic nerve ; (3) the area 

 within the stalk wdiich is occupied by several difierent structures, bemg 

 shut oft' in front from the retinal chamber by a sharp line wdiich is 

 the edge of the basilar membrane (B. m.), and on the sides by a 

 second sharp line parallel with the epidermis, the hypodermis (h). 

 which may be interrupted in places or pulled aw^ay from the cuticle in 

 the process of preparation of the section ; (4) the central part of the 

 stalk occupied by the optic nerve (o.n.) and optic ganglion (g.n.) ; 

 (5) the bands between the nerve stalk and the hypodermis running length- 

 wise of the stalk, the eye-tmiscles (m). These various parts of the eye 

 once located, we can applv the high powder to a studv of the various 

 positions in detail. 



3. Histological study with the high power. 



I . The epidermis of the stalk, which should be examined before that 

 of the retinal chamberof the eye. is found to be of very considerable thick- 

 ness and deeply stained in its outer portion, but only faintly within. 



