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 may be 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 
