450 DR THOMAS H. BRYCE ON 
spaces between them. These are either of the mononuclear type or, more frequently, 
show various degrees of polymorphism, and a large number have their protoplasm filled 
with granules. Further back, the tissue over the surface of the yolk has the same 
characters, and in certain situations, as at the point marked M in text fig. 2, it has 
the appearance represented in fig. 22, Pl. II. Above is the line of the mesepithelium, 
below and to the left is the yolk-laden hypoblast. Directly continuous with this the 
mesenchymatous tissue is composed of a network of protoplasmic threads, in the meshes 
of which are cells showing all degrees of polymorphism in their nuclei, while in the 
deeper layers near the hypoblast there are numerous cells with the protoplasm laden 
Fic. 5.—Section through larva, stage 32+, at level of the hind- 
limb buds, 
A, aorta ; C.V., cardinal vein ; Pr., nephric duct between 
Pr. and A, the tract of mesenchyme lettered N in preceding 
figures ; G, solid hind gut. 
with fine granules. The nuclei of the cells forming the framework are widely 
separated, and are thus apparently fewer in number than the free cells. They are 
elongated like the nucleus above and to the left (bounding here a space containing 
two erythrocytes), or rounded like those below, between the two horseshoe-shaped 
nuclei. 
In other portions of the tissue the general characters are the same, but the poly- 
morphic metamorphosis of the nuclei is not everywhere so pronounced, and large 
mononuclear free elements are more numerous. Throughout this tract of mesenchyme 
mitotic figures are of frequent occurrence. 
