THE (ESOPHAGUS, STOMACHS AND INTESTINES. 413 



Each tube consists of a basement membrane enclosing a 

 number of cells ; these cells measure about 50 /JL in diameter 

 and give the tubes, which are only about 75 yu, 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 : 



(i) 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 



