1887.] MICROSCOPICAL JOURNAL. 125 
gland, as usual. The gland, then, is made up of bags or alveoli, closely packed 
together. These alveoli are thin walls, one cell thick, covering in considerable 
spaces. The walls are, further, not simple, but thrown into numbers of folds, 
which run into the cavity of the alveoli, thus increasing the wall space or giv- 
ing place fora greater number of cells. Sometimes these ingrowing processes 
are sharp-pointed, and when cut in sections they show no sign of their con- 
nection with the wall, this showing in sections at some other level. The blood 
space is the space around the alveoli, which do not open into the blood space, 
as is evidenced by the entire absence of blood corpuscles from their lumen. 
The foldings of the walls are separated and the blood space continues into 
them, as shown by the presence of blood corpuscles; and the same is true 
of the centres of the ‘islands.’ The alveoli are of three kinds, as shown by 
the character of the cells which form their walls. The manner in which these 
are connected with each other is not shown by the section, and would require 
a completer study of the structure of the organ than is at present desirable. 
The fact that they do open into each other may be demonstrated in various 
places. Thus, in figure 1, is shown the communication between the collect- 
ing sack and a cubical cell-lined alveolus, which is undoubtedly the main out- 
let from the various alveoli throughout the gland. In a section not far from 
the one figured the upper end of the duct opens into the large alveolus just 
above it in figure 1. 
The green gland, then, is made up of a sack lined with flat-celled epithe- 
lium opening into the gland proper, and the gland made up of alveoli or les- 
ser sacks of three kinds, which communicate with each other and are 
surrounded by blood spaces, through which blood corpuscles wander at large. 
This, with the particular account of the cells, is the interpretation of the 
appearances seen in a study of the section; itis by no means all which would 
be likely to be thought of by the most thoughtful and practised students, but 
it is the least which should be thought of by any one who would place him- 
self in the attitude of a student of histology. It implies more than merely 
the cutting of a pretty section. It supplements the merely mechanical oper- 
ation with the proper biological one; the studying out of the section and the 
reproduction from it of the facts as to the actual structure of the organ under 
consideration. It is a wonderful result to be able to preserve these delicate 
and perishable bodies—cubes of ;5!59 in. in diameter—to slice them up and 
mount them permanently, so thata hundred years hence any one might accu- 
rately measure and draw their shape and get a result which the careful use 
of the technical methods at present in use makes possible and even easy.* 
Key to the Rotifera.—III. 
By L. C. STEVENS. 
(Continued from page og.) 
39. MASTIGOCERCA. 
( Zoe usually with accessory basal stylets.) 
a. Stylets none; toe two-thirds body-and-head length ; base bulbous, 
bicornis. 
a. Stylets none; toe less than one-half body-and-head length, simple, 
stylata. 
6. Stylets very minute; toe equal to body-and-head length, straight, 
carinata. 
* If the above account, full as it is, leaves some points unsettled, e. ¢., the membrane which envelopes the 
gland and sack, the communications of the blood-space with the body cavity, and others, it is not because they 
are not important, but only because they must be omitted for the present. 
