402 Proceedings of Royal Society of Edinburgh, [june 18 , 
Darwin states, in The Origin of Species (chap, vi.) : — “Numerous 
cases could be given among the lower animals of the same organ 
performing at the same time wholly distinct functions : thus, in 
the larva of the dragon-fly and in the fish Cobites, the alimentary 
canal respires, digests, and excretes.” 
The author has found that in the mature or perfect form of 
the dragon-fly, the Malpighian tubules function as true kidneys. 
The Malpighian tubules in Lihellula depressa (fig. 1) number from 
60 to 70, and are unhranched. 
Fig. 1. — Dissection showing the Malpighian Tubules of Libellula 
depressa (natural size). 
Under the microscope, a Malpighian tubule is seen to consist of a 
connective tissue layer, a delicate “tracheal tube,” a basement 
membrane, and lastly, an epithelial layer of comparatively large 
nucleated cells (fig. 2). The internal cavity of one of these tubules 
is very irregular, as is seen by examining various parts of it in 
transverse section. 
The author has extracted uric acid from^ the secretion of these 
tubules in the following manner : — 
(1) A large number of Malpighian tubules were boiled in distilled 
water and filtered. The filtrate was evaporated carefully to dryness 
on a water-bath. 
The residue so obtained was treated with absolute alcohol and 
filtered. Boiling water was poured upon the residue, and to the 
aqueous filtrate an access of pure acetic acid added. After standing 
all night, crystals of uric acid (CgH^N^Og) were deposited. When 
