382 Dr. Burnett on the Renal Organs of the Vertebrata. 
and around these subdivisions are collected a mass of blastematous 
cells. These cells serve as the material for the growth and further 
division of the tubes—in fact for their ultimate ramification, until 
the whole structure is completed. There is observed, therefore, at 
an early period, a main stem (ureter) which has many branches, 
each of which is the foot-stalk of a leaf-like body ; this last is one 
of the future lobules of the kidney. ‘Mhe whole plan of structure is 
here lai®out—a branching ureter with lobules. The increase of the 
size of these lobules, and the formation of the ultimate uriniferous 
tubes takes place by one and the same process, viz.: by the 
branching of the original tubes in a plumate form from a main 
tube,—the whole resembling the plume of a feather. The tubes 
do not end, however, on the edge of the plume (so to speak), but 
here loop and return, and when near the shaft or main tube, they 
dilate into Malpighian bodies; this is, as far as 1 have observed, 
their invariable mode of termination, there being no auastomoses 
of the tubes as some have supposed. : 
The mode of formation of the Malpighian body of the true kid- 
ney, is precisely like that of the same structure belonging to the 
Wolffian body, already described; I need not therefore here re- 
peat the description. I may remark, however, that the two blo 
vessels which compose the glomerulus, usually penetrate the cap- 
sular dilation of the tube at some point more or less near the op- 
posite one of its insertion upon the tube, and rarely more laterally, 
or at least on the inner half of the capsule. In the chick, the 
Malpighian bodies begin to appear at about the tenth day; they 
are then very few in number, but they become more numerous 
exactly in proportion to the growth of the organ—not ceasing 10 
be formed until the kidney has reached its full size. : 
Nothing could be simpler therefore than the mode of formation 
of the renal structure; it is clear and unmistakable—one tube 
_ gives rise to another by an eversion of its walls, aud this last pro- 
duces another in the same way, and so on. , 
Such is the mode of development as occurring in Birds, and 
my observations upon it as found in all the other classes, show 
that the formula is there invariably the same. There are, how- 
ever, peculiarities of the combination of this formula ™ each 
class, which demand a special consideration. cht 
In Fishes, these organs appear at an early period as two straigh 
-tubes, extending, one on each side of the vertebral column, i 
the region of the heart to the anus. These tubes soon g!v@ oh 
from their inferior and inner surface, deverticula, exactly a8 W! 
the Wolffian bodies just described, and for a time the organs pis 
much the same appearance as embryonic kidneys. But ak - 
wards, as the animal increases in size, a new development tas 
place. This consists in the branching, dichotomously, Oe. 
deverticular tubes,—a process which goes on indefinitely, giving 
a - 
