THE DEVELOPMENT OF THE LYMPHATIC SYSTEM IN 
RABBITS. 
BY 
FREDERIC T. LEWIS, A.M., M.D. 
From the Embryological Laboratory, Harvard Medical School. 
WitH 8 TExT FIGURES.? 
In following the transformations of the subcardinal veins in rabbits, 
the writer observed that a portion of those veins seemed to become de- 
tached from the venous system, and to be transformed into lymphatic 
vessels (02, p. 238). This supposition is not identical with the theory 
that the lymphatic system is a gland-like outgrowth of venous endothel- 
ium, always connected with the veins by means of the lymphatic ducts. 
It differs also from the older idea that lymphatic vessels are excavations 
in mesenchyma. 
In favor of this mesenchymal origin, the work of Sala, 00, is the most 
convincing. He observed in the chick that both the posterior lymph heart 
and the thoracic duct arose independently of the veins or of other lym- - 
phatics, and that their permanent openings into the veins were acquired 
subsequently. In the rabbit, as will be shown presently, there are many 
disconnected lymphatic spaces, but to their origin from mesenchyma there 
are four objections: 1st. The lymphatic spaces do not resemble mesen- 
chyma even when it is oedematous, but on the contrary, are scarcely dis- 
tinguishable from blood-vessels (Langer). 2d. After being formed, the 
lymphatics increase like blood-vessels, by means of blind endothelial 
sprouts, and not by connecting with intercellular spaces (Langer, Ranvier, 
MacCallum, Sabin). 3d. In early embryos, detached blood-vessels may 
be seen without proving that blood-vessels are mesenchymal spaces. These 
detached vessels are not far from the main trunks, from which they may 
have arisen by slender endothelial strands, yet often the connecting 
strands cannot be demonstrated. A similar supposition would account 
for detached lymphatic vessels. 4th. The endothelium of the embryonic 
lymphatics is sometimes seen to be continuous with that of the veins. 
1This investigation, and the one which follows, were accomplished with 
the aid of a Bullard Fellowship, established in memory of John Ware. 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
