THE MALPIGHIAN CORPUSCLES. 771 



which occupies about two-thirds of the diameter of the membranous 

 tube. The epithelial cells have very delicate walls, a roundish nucleus, 

 fine granular albuminoid contents, and occasional fat, pigment, and 

 other particles. This epithelial layer is continuous with that covering 

 the free surface of the papillae. In the cold-blooded Vertebrata, it is, 

 in parts, provided with cilia. 



The MalpigTiian corpuscle* of the cortical substance are placed 

 either at the free closed extremities of the convoluted tubuli, or in the 

 course of the loops which these occasionally form. These little bodies, 

 the glomeruli of Ruysch (1660), are spheroidal, and measure about 

 T |(jth of an inch in diameter. Each is composed of a rounded, close 

 coil of minute vessels, which projects, like a little ball, into one of the 

 capsules of the tubuli. It appears that a minute branch of the renal 

 artery, named an afferent vessel, reaches each Malpighian body, and, 

 dividing into superficial coiled branches, forms a globular network ; 

 from the centre of this an efferent vessel arises, and, leaving the cor- 

 puscle, forms, with the efferent vessels from neighboring corpuscles, a 

 dense vascular plexus, which surrounds the contiguous tubuli. Ac- 

 cording as the capsule of the Malpighian corpuscle is formed at the 

 commencement, or the side of a tubule, it is said to be lateral or terminal. 

 At the mouth of the capsule the spheroidal epithelium of the tubule 

 loses its character ; for within the capsule the epithelium is squamous 

 and remarkably thin. It is said by some to be continued over the 

 surface of the Malpighian corpuscle which projects into the capsule. 

 (Gerlach, Isaacs.) But according to Bowman the corpuscle lies naked 

 in the capsule, without any such covering, the afferent and efferent 

 vessels being supposed to perforate the capsule. These vessels enter 

 and pass out at nearly the same part of the corpuscle, which is there 

 attached to its capsule. According to some observers the efferent 

 vessel is always narrower than the afferent one, and hence has arisen 

 the idea that the blood is checked, or held back, in the coiled vessels 

 of the corpuscle. The central vessels of the corpuscles are, by some 

 physiologists, regarded as capillaries, and the efferent vessel as a vein, 

 which then breaks up to form the fine plexus around the adjoining 

 tubule an arrangement supposed to represent, on a very minute scale, 

 a renal portal system. But all the coiled vessels, and even the effer- 

 ent vessel of the Malpighian corpuscles are, by others, considered to 

 be arterial, the whole forming a microscopic rete miralile, which ulti- 

 mately, by the efferent vessel, ends in a true capillary network around 

 the tubules. 



The renal or emulgent arteries, right and left, spring from the sides 

 of the aorta ; they are short, and very large for the size of the kid- 

 neys, being out of proportion to the mere nutritive necessities of these 

 organs. They soon divide into four or five branches, which pass be- 

 tween the pyramids, and are partly distributed in the form of nutrient 

 vessels, to the cortical and medullary substances, and to the common 

 coat of the kidney ; but they chiefly terminate in the Malpighian cor- 

 puscles, or in the fine vascular network which surrounds the tubuli. 

 The veins accompany the arteries, and end, for each kidney, in a 

 single large renal or emulgent vein, which joins the ascending vena 



