THE AMERICAN 
MONTHLY 
MICROSCOPICAL JOURNAL. 
Vor. VII. MAY, 1887. Nase 
Elementary histological studies of the Cray-fish.—I. 
By HENRY L. OSBORN. 
INTRODUCTION. 
It is the purpose to prepare a series of studies upon the histological struc- 
ture of the cray-fish, presenting an introduction to the science of histology 
for the use of those beginners who require a guide of an elementary character. 
In setting forth the subject I shall attempt to omit no detail of instruction, in 
regard to both the method of manipulation required, and, more particularly, 
the proper way to study histology; how to see, and what to see; how to 
interpret one’s observations ; and, last, but not least, how to record the obser- 
vations, both by drawings and by written descriptions. 
The study of histology may be desultory or scientific. The worker may 
collect section after section, give it a hasty glance, and store it in his cabinet— 
too often he does only this—or he may thoroughly examine his section, and 
from it go to its place in the organ of which it forms a part, to build up for him- 
self a competent idea of the construction of the organ. This should always 
be his purpose, and it is to teach such a method of working in histology that 
this series of studies in the histology of the cray-fish is laid before our readers. 
If they prove helpful to biological teachers as well, it will be an added gain, 
for there is a need of some work to be used as an elementary guide in animal 
histology. to accompany the many elementary works on zoology from which 
this chapter is omitted. My reasons for selecting the cray-fish as the creature 
upon which to make these studies are several :—the great abundance of cray- 
fish in all parts of the country is one consideration, the general use of the 
cray-fish in anatomical studies is another; but the chief reason is that the 
greater simplicity of structure in the case of many of the organs makes them 
more favorable for a beginner to study than would be a vertebrate, while, at 
the same time, in the cray-fish the tissues are more varied than in lower forms, 
so that they illustrate well many of the facts and principles of animal his- 
tology. ; 
CHAPTER I.—THE GREEN GLAND. 
1. Gross anatomy.—lIt should be the invariable rule of the histologist to 
examine the part to be studied first with his naked eye, and also to familiarize 
himself with so much of it as can be seen with a simple microscope, for very 
often such precaution will save him a large amount of useless speculation 
regarding appearances which he finds presented in his section. Such an 
examination in the case of the green gland should be made as follows :—Place 
