446 DR THOMAS H. BRYCE ON 
In the vessels in the liver there are numerous cells identical with the free mesenchy- 
matous elements, and it is to be noticed that the spaces in the mesenchyme are continuous 
with the venous spaces in the liver. 
Turning to the somatic mesenchyme *—there is round the pronephric duct and 
mesonephric=tubules a specially cellular tract (fig. 21, Pl. II.), which is becoming 
canalised, as it were, from before backwards, to form irregular venous spaces round the 
tubules, as I shall show immediately. The section drawn (fig. 21) is far back in the 
SSS ine 
fr 
L.. 
Y 
Fic. 1,—Section through larva, stage 82+, behind heart, but in front of undifferentiated yolk cells. 33d. 
A, aorta; L, lung; Li., liver; Pr., pronephros; G, glomerulus: S, gullet; P.V., vena advehens of liver; 
H.V., vena revehens of liver ; Y, mesenchymatous tissue covering anterior surface of mass of undifferentiated yolk cells. 
series, and the tissue is not yet here penetrated by spaces containing blood corpuscles, 
but some of the cells seem to occupy spaces in the protoplasmic meshwork, and a few 
have polymorphic nuclei. The venous spaces naturally communicate with the cardinal 
vein, and these vessels contain cells, having again all the characters of the free elements 
in the mesenchyme. ‘This tract of mesenchyme is the rudiment of the lymphoid tissue, 
so called, of the kidney. This has long been well known as a seat of blood formation in 
* While it is quite legitimate to call the cellular tissue round the gut and on the mass of yolk cells mesenchyme, 
it is perhaps not strictly correct to use the term as applied to this tissue. I use it in quite a general sense as 4 
convenient word to indicate the young connective tissue. Through the whole larval stages the so-called lymphoid 
tissue is mesenchyme in this sense, with free cells in its meshes. 
