THE ESOPHAGUS, STOMACHS AND INTESTINES. 413 
Each tube consists of a basement membrane enclosing a 
number of cells; these cells measure about 50 » in diameter 
and give the tubes, which are only about 75 mw in diameter, a 
somewhat moniliform character. 
Transverse sections show only one or two cells in each, 
with a narrow channel, which is usually crescentic, between 
them. The cells are vacuolated with irregular cavities, and 
contain oil and pigment granules and minute colourless particles. 
The portion of the cell nearest to the wall of the tube consists 
of reticular protoplasm, and contains the nucleus ; that portion 
of the cell next the lumen is frequently seen to be partially 
dissolved, and often exhibits the appearance of being bounded 
by ragged fringes. 
The distal or blind ends of the tubules contain smaller cells, 
and have a narrower lumen than the end nearer the intestine. 
The ducts of the glands are lined with rodded cubical epithelium 
similar to that of the salivary (lingual) glands. 
The tubes and their contents are rendered intensely black 
by osmic acid, and the secretion contains minute fatty granules 
as well as pigment granules. 
The Malpighian tubules have been described as urinary 
organs by all modern authors; formerly they were regarded 
as hepatic or liver tubules. It appears to me that their 
relation with the intestine is entirely adverse to the modern 
view, and that they ought rather to be regarded as a hepato- 
pancreas. 
Schindler [165], in an elaborate paper, maintained the theory 
that they are analogous to the kidney tubules, and gives the 
following arguments in favour of this view: 
(1) They are developed from the proctodeum, and open into 
the rectum. (2) They appear at a very early period of 
development, when a liver would be useless, but when a renal 
organ would be of functional import. (3) They agree with 
kidney tubules in anatomical and_ histological characters. 
(4) Their secretion contains urates; and (5) Their secretion 
agrees in no way with the bile of other animals. 
I shall examine each of these statements in detail, and shall 
