416 THE ALIMENTARY CANAL OF THE IMAGO. 



substance (other than cholalic acid) gives the test so readily 

 except a naphthol. 



Nothing can exceed the beauty of this reaction on the 

 Malpighian tubes of the feeding larva ; but the result is less 

 definite in starved resting larvae, such as are sometimes 

 obtained in the winter months from shops where fishing-tackle, 

 etc., are sold. 



With regard to the statement that glycogen is absent, it 

 should rather be, the presence of glycogen has not been 

 proved ; but how anyone could expect to prove its presence 

 is more than I can understand. The cells of the Malpighian 

 tubules contain so much granular pigment that the iodine test 

 is inapplicable. Lastly, the statement that the tubules yield 

 no ferment can only be regarded as an assertion. The absence 

 of a ferment is not easily proved. I find that the Malpighian 

 tubes of the larva are powerful agents in the emulsification of 

 oil. By rubbing up a minute drop of oil in water on a glass 

 slip, it is quite possible to form an imperfect emulsion ; but 

 the granules are not long in reuniting ; if, however, a fragment 

 of a Malpighian tubule of the Blow-fly larva is added a very 

 perfect milk-white permanent emulsion maybe easily produced. 

 This evidence of the existence of an emulsive ferment is at 

 least as good as that on which the existence of a ferment has 

 been denied. 



Lastly, the remarkable rodded epithelium at the lower 

 extremity of the tubules indicates a secreting function, and its 

 similarity to that of the sericteria and of parts of the intestines 

 is in favour of the view that these tubules secrete a zymotic 

 fluid. 



When I stated that the Malpighian tubes are probably 

 hepatic in function, I only intended to indicate that they are 

 digestive glands, and not kidney tubules. I have no objection 

 to regarding them and the ' so-called ' livers of Crustacea, 

 Arachnids and Molluscs as pancreas-like glands. I do not 

 know what constitutes a liver; if it is the presence of cholalic 

 acid and glycogen, then as I am inclined to think cholalic acid, 

 or some nearly allied body, and glycogen are both present in 



