86 THE AMERICAN MONTHLY [ May, . 
seen running into the centre of the gland, and a change in the epithelium is 
seen. The whole body of the gland is, furthermore, found to be made up 
of cavities bordered with a very clearly-shown lining, which looks more or 
less like the lining of the duct. A somewhat close inspection of these cavi- 
ties will show that they are all closed, that is to say, if you begin at any one 
point, and follow the border around, you will come back at last to the very 
point from which you started. This may be demonstrated more clearly upon 
the figure than in all parts of the section, unless the section is very thin and 
perfect, but it can be shown clearly in so many parts of the section, and is so 
clearly indicated in others, that the observer can assure himself of its truth for 
all parts. In making such an excursion around the wall of some of the cavi- 
ties (thus, for example, the one in which the letter E is placed), it will be 
seen that the wall is very complicated, and in some places double, while in 
other places it is single. <A little reflection will show that we may regard 
the double places in the wall as inward folds from the single-rowed outer 
partition. Such folds in the walls of organs are very often met with in ani- 
mal structures, and they give a greater exposure of surface in a given area 
than simple walls without the folds would do. In E, as well as in another 
large cavity with the infolded walls, I have traced around a very dark 
boundary line, which will aid in following the folds. By following this line 
closely, spaces of greater or less extent will be found, and these, in many 
cases, will be seen to open out into a general space, which surrounds the 
whole cavity, and many other cavities. The cavity is known as the lumen 
of one of the gland sacks, and the cavity outside the wall is in direct com- 
munication with the general cavity of the body, the space inside the shell and 
Prats I1V.—Green gland of Cambarus tmmuntis. 
ee ee a 
