60 
MR. BOWMAN ON THE STRUCTURE AND USE OF 
mitted into the capsule besides blood-vessels. It is subdivided into as many lobes 
as there are primary branches of the terminal twig- or afferent vessel, and these lobes 
do not communicate, except at the root of the tuft. There are, therefore, deep clefts 
between them, which open when the lobes are not greatly distended with injection 
or blood. The surface of the tuft is everywhere unattached and free, and continuous 
with the opposed surfaces of the lobes. The whole circumference of every vessel 
composing the tuft, is also free, and lies loose in the cavity of the capsule. These 
circumstances cannot be seen in specimens gorgedwith injection, but only by careful 
examination of recent specimens with a power of 200 or 300 diameters. The vessels 
are so perfectly bare, that in no other situation in the body do the capillaries admit 
of being so satisfactorily studied. It is only where the tuft is large, as in Man and 
in the Horse, that its lobulated character can be always discerned. When the 
number of primary subdivisions of the afferent vessel is smaller, the detection of lobes 
is less easy. They may often be seen, however, in the Frog. In Birds and Reptiles, 
the afferent vessel seldom divides, but dilates, instead, into a pouch-like cavity, which, 
after taking two or three coils, contracts again and becomes the efferent vessel. 
Here of course there are no lobes ; but the surface of the whole dilated part is free. 
The basement membrane of the uriniferous tube, expanded over the Malpighian 
tuft to form its capsule, is a simple, homogeneous, and perfectly transparent mem- 
brane, in which no structure can be discovered. It is perforated, as before stated, by 
the afferent and efferent vessels, and is certainly not reflected over them. They are 
united to it at their point of transit, but in what precise manner I have not been able 
to determine. Opposite to this point is the orifice of the tube, the cavity of which is 
continuous with that of the capsule, generally by a constricted neck. I have speci- 
mens prepared with the double injection showing this continuity in Mammalia, Birds, 
Reptiles and Fish ; and, in Mammalia and Reptiles, I have obtained the still more 
satisfactory proof afforded by a clear view of the whole of the textures magnified 300 
diameters. As the Malpighian bodies are placed in every possible direction, it often 
happens that a thin section, parallel to the neck of the tube, cannot at once be ob- 
tained : but with perseverance this may always be done. The capsule is then seen 
to pass off into the basement membrane of the tube, as the body of a Florence flask 
into its neck. The basement membrane of the tube is lined by a nucleated epithe- 
lium of a finely-granular opake aspect, while the neck of the tube and its orifice be- 
come abruptly covered with a layer of cells much more transparent, and clothed with 
vibratile cilia. The epithelium is continued in many cases over the whole inner sur- 
face of the capsule ; in other instances I have found it impossible to detect the 
slightest appearance of it over more than a third of the capsule. When fairly within 
the capsule, the cilia cease, and the epithelium beyond is of excessive delicacy and 
translucence. Its particles are seldom nucleated, and appear liable to swell by the 
addition of the water added to the specimen. They frequently fill up the space be- 
tween the capsule and tuft, and touching the latter, may seem to be united to it. 
