\ 
384 Dr. Burnett on the Renal Organs of the Vertebrata. 
lies, it is evident that the development is arborescent, forming 
lobules,—and these lobules are at first exactly like those observed 
in Serpents and Birds. In some species, as is well known, these 
lobules remain distinct through life; this is well seen in the otter, 
bear, and whale, and in many of the Ruminantia, these remains 
are distinctly visible. It is only in the higher forms, that they 
have so coalesced as to be concealed. 
This intimate combination of parts produces the greatest 
amount of secreting surface in the smallest space. Take, tor 
instance, the kidney of Man; here the lobules are arranged in a 
half-circle around a common cavity or the pelvis. But they are 
so united as to become conical in shape (with the bases of the 
cones at the surface of the organ) thereby producing the so-called 
pyramids. + These pyramids are composed in part of tubes that 
spread out in a fan-like manner from a common point (calyx), and 
the gradually increased size of the medullary portion is produce 
by the branching of the tubes in a dichotomous manner. The 
straight regular way in which these tubes run, seems to be dne, 10 @ 
measure at least, to the mechanical pressure to which they are sub- 
jected by the combination of the lobules,—for I have been unable 
to perceive it in very young embryos, and, moreover, it does not 
‘ agree with the invariable arborescent conditions of early forma- 
tion. The so-called Medullary portion of the kidney is made 
up of fasciculi of straight tubes which divide dichotomously, 
but have no Malpighian bodies; they continue directly to the 
Cortical portion which is composed of more or less convoluted 
tubes—the result of the dichotomous division. These tubes 
finally end, each, in a Malpighian body. ‘These Malpighian 
bodies sometimes lie upon the surface, directly beneath the ¢ap- 
sule, but often also the tubes run up to the surface, loop, return @ 
short distance, and end in a Malpighian body deeper in the.renal 
structure. From all I have observed, it appears that in Man the 
Malpighian body is the on/y termination of the final tubes, there 
being therefore as many of the former as of the latter. I have 
seen nothing like an anastomosis of the final tubes, as some re 
] = 
supposed is sometimes the case. The pelvis of the human 
ney, as also that of other mammals, is formed by th 
of the main duct, or ureter, involving the primary brane 
give off the straight tubes of the medullary substance. In 
way, and by the union of the bases of the pyramids, the ap 
are left free, projecting into this pelvis or main cavity. - 
changes I have 6njoyed an opportunity to trace in an embryo 
_ It will be seen, therefore, that the development of the kidney 
in Man and the higher mammals involves no new phases—t 
differences of general structure being extrinsic and due toon 
binations which produce compactness and decreased size withou 
a corresponding decrease of functional surface. sa 
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