fl OTTO F. KAMPMEIER 
are stuffed with large yolk globules from tip to tip—a fact that 
clearly distinguishes them from the surrounding mesenchymal 
cells which have for the most part lost their yolk content. The 
nuclei of incipient endothelium, regardless of whether haemal or 
lymphatic, show no difference, except possibly in chromatic 
density when compared with those of mesenchyme; indeed, the 
endothelium presents a very unspecialized appearance. The 
fact of the longer retention of yolk spherules by the cells of vas- 
cular anlagen and channels was reported by the author (15) and 
emphasized as a diagnostic trait of considerable value in dis- 
criminating between these tissues during the earlier embryonic 
period. Their distinctions were accurately expressed in the 
colored figures of that paper, to which the reader is referred. 
The next older stage, a 6-mm. embryo, is characterized by the 
numerical increase of sinus anlagen along the external jugular 
veins, by their growth in length and budding of branches, their 
detachment from the venous intima at the original point of con- 
tact, and by their acquisition of lumina. The reconstruction in 
figure 29 displays the number, size, form, affinities, and distri- 
bution of these lymphatic anlagen. It furnishes a convincing 
picture to show that the sinus does not originate by centrifugal 
sprouting from any specific foci, but that it has a multiple origin 
in proximate relation with vessels of the primitive vascular net- 
work, and that the initial anlagen are discontinuous. Further, 
it shows the bilateral origin of the sinus and also that its principal 
or mandibular division is the first component to be formed, the 
other divisions, such as the circumoral, temporal and pericardial 
appearing somewhat later. 
The time at which the individual lymphatic anlagen that are 
adherent to the venous wall retract from it varies greatly, neither 
the time of their beginning nor their length entirely conditioning 
it. In the reconstruction (fig. 29) some of them still cling to the 
blood channel, while others, even smaller ones, lie independently 
in the surrounding tissue. Nor is the size of the anlage a cri- 
terion of the possession of a lumen; one may acquire such very 
early, even in its incipient stage, while another may remain solid 
for a longer period of time. When a lumen does appear, it is at 
