THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. IX. FEBRUARY, 1888. No. 2. 



Elementary histological studies of the Cray-fish. — YIII. 



By henry L. OSBORN. 



CHAPTER III. — THE 'INTESTINE.' — (^Coritiiiiied from Vol. VIII, p. 20J.) 



I. Introductory. — I may beg the reader's consent to a tew prefatory re- 

 marks before beginning upon this third chapter of our elementary study in 

 histology. In the first place, for the information of any who may meet this 

 series of articles for the first time, with their perusal of the present part of 

 them, I would say that the purpose of the series is twofold : — to furnish the 

 general reader an exposition of the nature and subject-matter of the study of 

 histology, and second, to prepare a series of articles which may be read 

 by the practical student as a guide and introduction to the study of animal 

 histological observation. In designing and pursuing this course on the 

 elements of histology, I have not thought it necessary to minutely detail a 

 course in microscopical technique which, valuable though it would, perhaps, 

 seem to be in this connection, would divert me from my main pui"pose. 

 Such a course in technique, moreover, may find a place in these pages at 

 some future time, though it is now very thoroughly and clearly given by a 

 number of writers. How to prepare a slide is the subject of a host of chap- 

 ters in a host of works. But how to observe, what to see, and what to pass 

 by, what to think about, v/hat is seen, and ho\'s$to gather up the results of 

 the observations, is a part of the matter usually imperfectly treated or totally 

 omitted in spite of its superior importance. My aim has, therefore, been to 

 study chiefly the slide, and the metho'd only as it is necessary to the study of 

 the slide. 



I will add farther and briefly, by way of review, and to show any new 

 readers the ground already gone over in these studies, that I have already 

 considered the structure of the green-gland and the liver of the Cray-fish. Of 

 these the former was found to be a glandular organ, made up of cavities, 

 which were closed in, except at one point of entrance, by a wall made of cells 

 cubical in outline, one layer deep, and seated upon a basement membrane ; 

 the cavities of the gland communicating with the interior by means of con- 

 nected passages opening into one common duct, which in turn opened upon 

 the base of the antenna. This gland further was surrounded by a membra- 

 nous capsule and so constructed that the blood could circulate upon the walls 

 of the cavities, but in no case pass into the cavities or through them and their 

 communicating ducts to the exterior. The consideration of the green-gland 

 introduces one to an organ of comparative simplicity, and teaches there many 

 of the first lessons which the histologist must master. A study of the liver 

 enforces these lessons by the observation of another organ of comparative 



