THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. X. FEBRUARY, 1889. No. 2. 



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 can Mo7ithly Microscopical Journal, Box 6jo, Washington, D. C. 



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Elementary Histological Studies of the Cray-fish— XII. 



By HENRY LESLIE OSBORN. 



HAMLINE, MINN. 



CHAPTER V. — THE EYE. 



It will be remembered, by those who have followed through from 

 the first this course in the Cray-fish Histology, that the design has been 

 rather to teach how to study histology than to fully elucidate the his- 

 tology of Cambarus. What has been said in describing the green- 

 gland, the liver, etc., has all of it been true so far as I am aware, but it 

 has in no case been the entire exhaustive truth. So many details enter 

 into the mechanism of even the simplest animal, and many are so mi- 

 nute, or for other reasons so difficult of demonstration, that they are 

 passed over by all elementary treatises. Many of them have been only 

 very recently discovered. It has been the aim throughout this series to 

 treat of such appearances in an ordinarily well-made section as can be 

 observed by any one, and of the interpretation of these appearances to 

 form a true mental picture of the real object. Since the articles are 

 written primarily to show microscopists how to become histologists, 

 much is included which does not interest the professional histologist. 

 This didactic style will characterize this chapter upon the eye, and sub- 

 sequent chapters on teasing and isolation in the study of muscle and 

 nerve. 



1. Preparation of the Slide. — The eve of the Arthropod is a far 

 more difficult subject to prepare well than anything we have as yet at- 

 tempted. In fact, so difficult is it that the best authorities upon its struc- 

 ture are at variance as to 'the finer points. Much of its more easily 

 learned anatomy is within the reach of any one, and will furnish, by 

 reason of its greater complexity than that of any organ thus far studied, 

 an admirable theme for one of the " elementary studies." If you examine 

 a live cray-fish you will see on either side of the long beak-like projection 

 at the front end of the body a sort of socket bearing a short stump, 



Copyright, 1889, by C. W. Smiley. 



