It is also possible, as Oesterlen has sup posed, that these corpuscles experience a certain course of development ; and that, in many cases, the very small corpuscles are very young and undeveloped ones : but, hitherto, I have not been able to observe facts import.. ing the certain existence of a continual deve lopment of the Malpighian corpuscles in the adult animal ; nevertheless, I cannot avoid mentioning that, like Oesterlen, I have seen in the spleens of animals little heaps (from 2 to 4-100ths line in size) of cells, which have no distinct cell walls, and which, poss.bly, have some relation to the formation of the splenic corpuscles. It seems quite certain that the spleen corpuscles are not developed from separate cells of the spleen pulp ; al though this view has lately been brought for ward in a singular manner by Heinrich.* points of bifurcation, or at their sides. (Figs. 527, 258.) This relation, which also obtains The Malpieian corpuscles are imbedded in the red spleen substance, and, with the ex ception of one point, where they are attached to arterial twigs, they are everywhere sur rounded by this substance. They are con nected to the small arteries and their twigs by short peduncles, like the berries of a bunch of grapes ; and, in such wise, that a small arterial trunk of from 2 to 4-100ths line, with its ramifications, supports 5 to 10 corpuscles. (Fig. 526.) The peduncles of the corpuscles are almost always small arteries, which pass to be distributed to them; but in less frequent instances, they are constituted by short pro cesses of the arterial sheaths, which are con tinuous with the membranous wall of the corpuscle. In this manner the majority of the corpuscles are essentially devoid of a peduncle, and sit immediately on the arteries at their a, wall of the corpuscle ; b, elastic fibres in the same ; c, sheath of the artery; d, dissolved middle tunic of the artery; e, elastic inner coat.
in animals, formerly appeared to J. Miiller as indicating the fact that the splenic corpuscles were hollow excrescences of the vessel-walls, or were imbedded in these latter. But if by this be understood, what MUller's plates and description imply, that the sheaths of the vessels, in their whole thickness, with all their elements, are continued to form the cor puscles, then it is certainly incorrect : for in some animals I have seen that, from the rich network of elastic fibres and muscular struc ture of these sheaths, little or nothing passes to the corpuscles : and I have generally found the membrane of the corpuscle very delicate. It is, however, quite conformable to truth, to state that this membrane has a direct con tinuity with the arterial sheaths. (Fig. 527, 528.) The corpuscles do not possess any con nection with the trabecular network, still less that which Gerlach has lately attributed to them : viz. that they serve as points of sup port to the elastic fibres of the partitions ; a belief which is altogether baseless.
It is difficult to say any thing definite re specting the number of the splenic corpuscles. Hessling believes that, in some cases, they constitute from one-fifth to one-sixth of the whole splenic mass ; and this seems to me no overstatement, if we substitute the expression " spleen-pulp " for " spleen-mass." At least, I have found, that their quantity is very considerable; and that in some instances, when they are rather turgescent, the whole pnlp appears as if besprinkled with white. They stand so thickly together, that in many places they touch each other's sides ; and in others are only separated from each other by narrow interspaces, which in the least favour able circumstances are about one to two lines in size. I believe that the estimate, that one and a half to two lines of spleen-pulp con tains one Malpighian corpuscle, is rather too little than too large.
As regards the lower animals, it would follow from my researches, that the Malpighian cor puscles occur in Manznidia in precisely the same way as in Man ; at least, in more than twenty genera which I have examined, I have never found them to be absent. It has long been known that they are very distinct in pigs, sheep, oxen, goats, and so also in guinea pigs, hedgehogs, and bats, dzc., in whom they are rather larger and more resisting than in Man; and although in the dog, cat, and rabbit, they are somewhat smaller and more covered by the pulp, yet they are nevertheless very dis tinct. As to Birds, Bardeleben seems to have recognised the Malpighian corpuscles in swal lows, pigeons, and geese ; while I have been able to verify their existence in sparrows, although they are not particularly distinct. So also Ecker briefly states, that he has seen them in birds ; and Oesterlen mentions their occurrence in the fowl, pigeon, and in many of the Rctptores. Amongst the Reptilia, J. Midler has detected them in the Chelonia ; while I have seen them very distinctly in the anguis fragilis, in whom the corpuscles were surrounded by a beautiful network of capil laries. Amongst the naked Amphibia, Oesterlen states himself to have seen them here and there in toads and frogs ; but in direct op position to this, I have found no trace of them. Just as little have I been able to de tect them in Fishes, although I have examined many of the fresh-water genera with this especial purpose. And thus the conjecture of Miller #, — that they exist in all the verte brata, although in none so distinct or so easy of o'oservation as in the vegetable-eating mammals —must be considered as incorrect : a cirumstance which is not without consider able interest in the determination of their import.
On inquiry into the more minute structure of the Malpighian corpuscles, it is exceedingly necessary to regard, not only their appear ances in Man, but also in the lower animals. Each Malpighian corpuscle possesses a mem brane and contents, and therefore is not a solid corpuscle, but rather a vesicle. The mem brane which Malpighi beheld, was minutely described for the first time by Miiller and Giesker. According to the first of these ob servers it is, as previously mentioned, a pro cess of the common sheath of the vessels, which either immediately continues as a ve sicular swelling of the satne, or is previously produced into a peduncle. Giesker rejects this view, at least as regards the human sub ject, and describes in each corpuscle a pecu liar, independent, and tolerably strong mem brane, which seems to have no connection with the sheaths of the vessels, but receives an additional thin outer covering of white fibrous tissue, in which the vessels of the cor puscle ramify, and to which they frequently impart their own red colour. The ma jority of later observers have unconditionally adopted one or the other of these views ; only a few of them, as J. Simon, Henle, Ecker, and Oesterlen, having taken the trouble of substantiating their truth by original inquiry. Henle, Oesterlen, and J. Simon, deny the existence of a special membrane. The first of these observers finds that the wall of the corpuscles is constituted solely of granules, under which appear to be comprised struc tures resembling the morphous part of the contents ; while fine bundles of white fibrous tissue unite on their outer surface. Oesterlen and J. Simon likewise deny the peculiar mem brane (limitary membrane), an absence which the latter associates with the capacity of the corpuscles to fill themselves out from the capillary vessels. So also Bardeleben de scribes a membrane very indistinctly.