246 



REN. 



root of the tuft. There are, therefore, deep 

 clefts between them, which open when the 

 lobes are not greatly distended with injection 

 or blood. (Fig. 153, i.) ; The surface of 



Fig. 155. 



Malpighian body, tube, &c., from the horse. The 

 injection has penetrated from the artery through 

 the Malpighian tuft into the plexus surrounding the 

 tubes. It has then ruptured the vessels of the tuft, 

 filled the capsule, and passed off along the tube, a, 

 arterial branch ; e, afferent vessel ; c, capsule dis- 

 tended; t, tube; /, efferent vessel; p, plexus of 

 capillaries, surrounding other tubes not injected. 

 Magnified about thirty diameters. (After Bowman.} 



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 

 gorged with injection, but only by careful 

 examination of recent specimens with a power 

 of 200 or 600 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. Where the number of pri- 

 mary 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. There are of course 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 

 transparent membrane, 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 Mr. Bowman has not 

 been able to determine. It appears probable 

 that the membrane is reflected to a slight ex- 

 tent upon the afferent and efferent vessels, 

 and that thus the union is effected. The 

 appearance of bulging presented by the dis- 

 tended capsule round the entrance of the 

 afferent vessels in fig. 156. seems to indicate 

 that the membrane is slightly reflected in- 



wards upon the trunks of the vessels, if this 

 term can be correctly applied to such minute 



Fig. 156. 



Two Malpighian bodies injected from the human 

 subject. The tufts are burst and the fluid has es- 

 caped into the capsule. In one case it has passed 

 also along the tube, the extreme tortuosity of which 

 at its commencement is well seen, a, arterial 

 branch ; /, terminal twigs ; c, c, Malpighian cap- 

 sules distended; e, the depression often seen in 

 such cases, at the point where the afferent and effe- 

 rent vessels pass : the latter are not here injected ; 

 t, the tube. Magnified about ninety diameters. 

 (After Bowman.} 



vessels as the afferent and efferent vessels of 

 the Malpighian bodies. Opposite to the point 

 where the vessels perforate the capsule, is the 

 orifice of the tube, the cavity of which is con- 

 tinuous with that of the capsule, generally by 

 a constricted neck. Mr. Bowman has speci- 

 mens prepared with the double injection, 

 showing this continuity in Mammalia, Birds, 

 Reptiles, and Fish. (fig. 157.) 



A more satisfactory proof of the direct 

 continuity of the cavity of the tube with that 

 of the Malpighian capsule is afforded by a 

 clear view of the whole of the textures mag- 

 nified 200 or 300 diameters. The capsule 

 may thus be seen to pass off into the basement 

 membrane of the tube as the body of a Flo- 

 rence flask into its neck (figs. 158. and 159.). 



The basement membrane of the tube is 

 lined by a nucleated epithelium of a finely 

 granular opaque aspect, while the neck of the 

 tube and the contiguous portion of the cap- 

 sule are covered by a layer of cells much 

 more transparent, and clothed with vibratile 

 cilia. The epithelium appears to be continued 

 in many cases over the whole inner surface 

 of the capsule, while in other instances it is 

 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 application of water to the specimen. 

 The cavity existing in the natural state be- 



