52 THE AMEKICAN MONTHLY [March, 



is a cut surface ; the dots represent fibres. The outline of the mesal 

 cavities is indicated by the heavy black line. The specimen was pre- 

 pared by slicing away the cephalic portion of hemi-cerebrum to a de2:)th 

 of about five millimeters. 



a. Olfactory bulb with its small rhinocoele entirely circumscribed. 



b. Olfactory crus ; its cavity is completely closed. 



c. Paracoele (lateral ventricle) . 



d. Medicom missure. 



e. Diacoele (third ventricle). 



f. Cerebral crus. 



g. Geminum. 



h. Mesocoele (aqueduct of Sylvius). 



Fig. 5. The rhinoccele of a dog, much enlarged, to show the intrusion 

 of the neuroglia into the cavity, and the break in continuity of the endy- 

 mal cells. 



Fig. 6. A section through the central portion of the olfactory crus of 

 a dog. The darker portion represents the axis, composed of broken- 

 down endymal cells, granules, etc. 



Fig. 7. A section through the olfactory crus of the coyote. The 

 endymal cells still remain, but the cavit}^ is entirely occluded. 



Fig. S. A section through the olfactory crus of the dingo. The cells 

 and cavity are as in fig. 6. 



A Method of Drawing Microscopic Objects by the Use of Coordi- 

 nates. 



By cooper CURTICE, D. V. S., 



MORAVIA, N. Y. 



[Read before the Washington Microscopical Society, 1891.] 



The method which I am to detail is one that I found in use by Dr. 

 George Marx, of the Division of Illustrations, in the U. S. Agricul- 

 tural Department, when I first engaged in studying animal parasites in 

 1S86, but it was originated some eight years eai'lier, as he informs me. 



It is a method that has such obvious merits that I take pleasure in 

 placing it before students of the microscope, but I present it as a re- 

 lator of a valuable method rather than of original work. Its simplic- 

 ity, its cheapness, its accuracy, the ease with which a figure of any 

 magnification or reduction may be made, and the rapidity with which 

 a beginner adapts himself to its use, all serve to recommend it. 



A small glass slide, of the size of an eye-piece micrometer, or a disc, 

 ruled into squares, is inserted into the eye-piece, so that the lines seem 

 to rest upon the object. Tracing paper is placed over cai^dboard ruled 

 into squares. The drawing is then made free-hand, the various points 

 being located in a symmetrical position with respect to the lines under- 

 lying the paper that they occupy in the apparently ruled image. 

 The drawing made on the ti'acing-paper may then be either transferred 

 to drawing-paper without reduction or be reduced by applying the same 

 methods that produced the picture and then be worked up. 



Dr. Marx prefers using the slide. It is ruled into squares one milli- 

 meter on each side, every third line being slightly deeper to make it 

 more prominent. I prefer for most uses the finder made by Zeiss. It 



