DEVELOPMENT OF BLOOD-VESSELS. 103 



by MM. Prevost and Lebert,* who, with Plattner, are of opinion that such 

 vessels are always formed centrifugally, and under the influence of the circula- 

 tion, by arches passing from a minute artery to a corresponding vein. These 

 arches, they state, are formed in spaces left by the separation of the cells of 

 the part in which the development of vessels takes place, and do not result 

 as Schwann and Kolliker describe, from the coalescence of the branches pro- 

 ceeding from cells. The circumstance which, in their opinion, has led to 

 the supposition of this latter being the true mode of formation, is the 

 resemblance to cells presented by the interspaces themselves. From 

 their observations on the development of the chick also,f Prevost and 

 Lebert arrived at similar conclusions concerning the formation of 

 blood-vessels. 



In the opinion of Vogt also, from observations made on the embryonal 

 salmon,{ blood-vessels invariably originate, not from the branching and 

 coalescence of cells, but as spaces or channels hollowed out in the midst of 

 the cell-substance of the part in which the development takes place. The 

 formation of these channels appears, however, in his opinion, to result from 

 a simple separation of the cells from each other, and, contrary to the view 

 of Plattner, Prevost, and Lebert, to be quite independent of the heart or the 

 rest of the circulation, with neither of which, indeed, have the channels at 

 their first formation, any communication. At first these channels are un- 

 provided with distinct bounding walls, but shortly there is observed a delicate 

 membranous lining to the canal, formed apparently by a layer of the cells 

 in the midst of which the new vessels are developed. This mode of de- 

 velopment, according to Vogt, is observed in the formation both of the 

 first embryonic trunks in connection with the heart, and of the finer vessels 

 or capillaries in other parts. That it prevails in the first case, is admitted 

 also by Kolliker, but that it does not, in his opinion, in the case of the 

 finer vessels, has been already shewn. 



The description which Kolliker has given of the process as it occurs 

 in the tail of young Batrachians, is doubtless the most correct one, and 

 it may, with every probability of truth, be assumed to represent the mode 

 in which blood-vessels are developed in all other tissues, and in all other 

 classes of animals. With Kblliker's account it is possible to reconcile the 

 descriptions furnished by Plattner and others, even though contrary to the 

 designs of the authors ; for with the exception of admitting the influence of 

 cells, their account of the gradual formation of arches by the junction and 

 coalescence of fine processes, and the gradual conversion of these into 

 permeable tubes, closely accords with that given by Kolliker. The de- 

 scription furnished by Vogt is, however, so much opposed to that of Kolli- 

 ker, that the difference must either be attributed to some misconception of 



* Ann. des Scien. Nat. 1844, p. 222. f Ann. des Scien. Nat. 1844, p. 265. 



J Hist. Nat. des Poissons, t. i. p. 206 ; and Entwickel. der Geburtshelferkrote, p. 7 1 . 

 Henle and Pfeufers Zeitschrift fiir rationelle Medizin, 1845-6. 



