1889.] MICKOSCOPICAL JOUBNAL. 29 



the basilar membrane. The single rods are illustrated in fig. 4, and 

 the different parts are called in Huxley's account, the (1) crystalline 

 cone, (2) the filament, and (3) the striated spindle. Careful examin- 

 ation of the rod will show at its outer end, in many places, a deeper 

 coloration, and perhaps demonstrate a couple of nuclei there (see fig. 

 6, from sections by second method). Running down the centre of the 

 crystalline cone in places can be faintly seen a very fine line. It can 

 rarely be traced the length of the cone. It indicates that the cone may 

 be composed of two halves. The striated spindle or pedicle cannot be 

 clearly seen in the section by the second method, for it is entirely sur- 

 rounded by certain investing matters. But the chromic acid method 

 displayed them in a very perfect manner with their connection with the 

 rest of the rod. In the corrosive sublimate preparations they can be 

 seen, though less distinctly. 



5. Pigment Cells. — On the sides of the crystalline cone can be seen 

 very plainly masses of dark, coarsely granular pigment, which more 

 careful study in various places will probably show disposed in long 

 narrow cells between the cones, cells which seem shorter than the cones. 

 In some slides these are plainly cells because their nuclei can be ob- 

 served. They together form (in good sections) a distinct zone, the 

 " outer dark zone," as it is called by Huxley. The individual cell 

 shapes are but poorly preserved in most sections, those by the second 

 method being compacted, as if by pressure, with the crystalline cones. 



6. Retinulce. — Surrounding the striated spindles, in the same way 

 as the pigment cells surround the crystalline cones, may be seen a 

 second set of greatly pigmented bodies forming a second "' inner dark 

 zone." Carefully analyzed, this is found to be made by a second set 

 of pigment cells embracing the spindle at this lower level. In the 

 chromic acid specimens these cells seem to be much contracted and 

 drawn down toward the basilar membrane, thereby displaying, in a 

 clear manner," the outlines of the spindles, and also, to a certain extent, 

 their own form. In the specimens by the second method the cells are 

 so compressed with the visual rods that neither can be clearly observed. 



7. Basilar Membrane. — At the back of the anterior chamber of 

 the eye the better sections will show a sharp line limiting this chamber 

 from the cavity of the stalk' (see B. m., fig. 1 and fig. 5.) This is a 

 connective tissue membrane which shuts oft' the retinal chamber from 

 the remainder of the organ. There is reason to suppose that it does 

 not shut oft' communication between these places in fact, for, though 

 it may not be observable upon your sections, it is believed to be a fact 

 that nerves pass through this membrane and into the visual rods. The 

 parts behind this membrane and a consideration of the proper interpre- 

 tation of these appearances will form the next number of this series of 

 articles. 



Section Staining by Fluids Mixed with Turpentine. — Prof. 

 C. O. Whitman {Am. Nat., v. 22, p. 1140) describes a process of 

 mixing staining substances dissolved in absolute alcohol with turpen- 

 tine, thus allowing the staining of serial sections after they have been 

 fixed to the slides and before being mounted in balsam. This method, 

 if it proves practicable, will be a great convenience in the preparation 

 of serial sections. 



