THE AMERICAN 
MONTHLY 
MICROSCOPICAL JOURNAL. 
Vor. VIII. JUNE, 1887. No. 6. 
Elementary histological studies of the Cray-fish.—II. | 
Biv EE NDR Your O!S BO} RIN: 
(Continued from page 87.) 
In the further study of the green gland a power of 350 diameters or there- 
abouts must be employed. The purpose of the study is to trace out more 
definitely the various elements which, placed together, form the organ whose 
position and shape have already been observed with the naked eye and with 
the low power. It is convenient to restrict the meaning of the word histol- 
ogy and apply it to the study of these various elements, their various shapes, 
and the way in which they are combined. The elements themselves are called 
the cells. ; 
Examination with the low power has already shown that all the substance 
of the gland inside the outer sheathing sack (J) is made up by cavities bounded 
by a wall and that the wall itself presents everywhere much the same look. 
Select the cavity in which the reference letter E is placed and examine the 
wall; the result is shown in figure 3. Here are to be seen, a, the blood space, 
b. c.;—6, blood corpuscles, bl. c., lying in the blood space ;—c, a sharp line which 
borders the body cavity, the basement membrane, b.m.;—d, a faint line running 
approximately parallel with the basement membrane, the outer cell wall; 
—ce, fainter lines running from the outer cell wall to the basement membrane, 
c. w., the side walls of the cells ;—/, finely granular matter in a dark zone 
near the basement membrane, the protoplasm ;—., a circular sharp line in 
the protoplasm bounding more colored matter, the nucleus, n. The skilled 
histologist looks for all these different parts at once ; notes which are promi- 
nent, which are indistinct, and makes many instantaneous inferences as to 
what must be the fact where the fact cannot be observed. And he finds it 
difficult to understand the beginner in his perplexity. Since some of the 
seven parts mentioned above are always easy to see and others are often to be 
known only by inference from indications of them rather than by observa- 
tion of themselves, I shall take up each one in course and discuss its appear- 
ance or how to see it. 
a. The blood space.—Spread all through the gland are spaces sais are 
in no case completely circumscribed. These spaces form a complete net- 
work of intercommunicating avenues, which traverse the entire structure. 
They are of very various shapes. They may be narrow passages between 
the cellular walls of the gland alveoli, where usually a few oval blood cor- 
puscles may be seen; sometimes so narrow that they are seen only as a faint 
line, or even obliterated for a short distance. In other cases they are broad 
open areas, usually containing much larger numbers of corpuscles. The 
blood spaces seem to be a place of resort for the corpuscles; in fact, they 
are the only portion of the gland in which they are ever found. The blood 
