Dr. Burnett on the Renal Organs of the Vertebrata. 377 
convoluted tube enclosing in its calibre smaller cells; this tnbe is 
the future blood-vessel which connects afierwards with the blood- 
vessels of the general circulation, and then the enclosed smaller 
epithelial cells become blood-corpuscles. ‘This convoluted blood- 
vessel is the so-called Malpighian tuft, or the Glomerulus, and is 
the functional or active structure of the organ. 
rief but comprehensive description of the structure of the 
Wolffian body would then be: a straight, main duct into which 
empty many digitiform tubes, the capsular dilatations of the free 
ends of which contain each a knot of blood-vessels. In the 
same way, I might describe the method of its function, as: the 
straining off from the blood, through this knot of vessels, those 
effete particles which as a whole form the uritiary excretion of 
the embryo. A structure more simple cannot easily be conceived 
of, yet its function is most effectual, for although thus quickly 
formed, we shall soon Jearn that both the structure and function 
of the complex permanent kidney rest upon precisely the same 
primitive types. 
‘These temporary kidneys, thus formed, which have, as before 
remarked, exactly the same structure wherever found, have a du- 
ration varying in the different classes, which stands in an inverse 
ratio to the grade of the animal. b 
In the true Reptiles, and in Birds, they persist as active func- 
tional organs during a considerable portion of the embryonic life ; 
dependent, vitelline life; thus, in the chick the kidneys assnme 
the urinary excretion at about the tenth (10th) day, yet the ves- 
tiges of those bodies may often be observed after hatching; and 
in the Alligator, I have seen, even four or five months after the 
animal had escaped the egg, the remains of these organs so well 
preserved that the Malpighian bodies were distinct in them. But 
in the Mammalia, where their existence as active parts is very 
brief, in fact so limited that it is difficult to observe them ina 
State of functional activity, they are correspondingly soon ab- 
sorbed, and although these remains are observed more or less dis- 
tinctly after birth in some species, yet, generally, they have 
Mostly passed away by the latter half of the intra-uterine life.* 
* Miller, (Physiologie, transl. by Jourdan, &c., Deux. éd. Paris, 1851, ii, p. 760, 
. C. 5.) bas gi g Wolffian body in 
& human foetus of 84 inches. As is well known, there may be observed during the 
t months of the human feetus, or even after birth, peculiar canaliculi situated in 
the n tube. They form the s ed or- 
of Rosenmiiller (De ovariis embryonum, Leipzig, 1501), and are probably the 
i olffian bod th inanti ipeda, and Suina, there are 
