294 ON THE STRUCTURE OF THE MALPIGHIAN BODIES 



the bodies assume, that the former do really pass through, and not 

 merely over, the latter. In Plate III. [Plate XXV.] (figs, i, 2, and 7) 

 I have represented the ordinary modes in which the arterial twigs are 

 disposed in the Malpighian bodies of the sheep (figs, i, 2) and of Man 

 (fig. 7). It should be observed, however, that the Malpighian bodies 

 have by no means always the well-marked oval outline which is here 

 represented. On the other hand they are very frequently diffuse and 

 irregular, sending out processes along the efferent and afferent twigs. 



The application of a high power, either to the compressed Mal- 

 pighian bod)-, or to one which has been torn out with needles and its 

 vessels isolated, fully confirms the results obtained by the previous 

 methods. In Man, the structure of the minute arterial twigs within 

 the bodies does not differ from that which they possess elsewhere 

 (fig. 7). Both the transversely .(smooth-muscular) and longitudinally 

 fibrous coats are well developed, neither being in excess ; and the 

 addition of acetic acid produces a clear line external to the former, 

 representing the innermost portion of the tunica adventitia, which 

 passes into, and is continuous with, the Malpighian pulp. The artery, 

 therefore, is not only surrounded by, and in immediate contact \\'ith, 

 the indifferent tissue of the pulp, but the latter, as Miiller pointed out, 

 is really the representative of a part of its tunica adventitia. In fact, 

 the indifferent tissue so completely forms an integral constituent of 

 the coat of the artery, that I could not, in any way, obtain the latter 

 free from it. 



In the Sheep, the arterial twigs have precisely the same relation 

 to the Malpighian pulp, but the intimate structure of their walls is 

 different, the circularly fibrous layer becoming almost obsolete, while 

 the longitudinally fibrous coat acquires proportionally increased 

 dimensions, and takes, at the same time, the structure of organic 

 muscle. In the small arterial twigs of i -Sooth inch in diameter,, 

 represented in fig. 3, the cavity of the vessels did not occupy more 

 than one-third of their diameter, and, like the efferent ramuscules, 

 unless they contained blood, they resembled mere trabecidcB, consisting 

 of organic muscle. 



The vessels within the Malpighian bodies are, however, not arterial 

 ramifications only : I find that there invariably exists, in addition, 

 a tolerably rich network of capillaries connecting the arterial ramus- 

 cules. These capillaries are vessels of i-ioooth to i-3oooth of an inch,, 

 or even less, in diameter, which can hardly be said to have parietes 

 distinct from the surrounding indifferent tissue of the pulp (figs. 3 

 and 8) ; unless they are filled with blood, indeed, they are not dis- 

 tinguishable with certainty ; and in the figures 2 and 7, I have, there- 



