, 
THE HISTOLOGY OF THE BLOOD OF LARVA OF LEPIDOSIREN PARADOXA, 451 
Somatic Mesenchyme. 
In the tract above mentioned the appearances differ according to the degree to 
which the tissue round the nephric ducts is opened out into venous spaces communi- 
eating with the cardinal vein. 
In the region of the pronephros (fig. 25, Pl. III.) the duct is surrounded by an 
irregular sinus, interrupted here and there by delicate protoplasmic strands, belonging 
to cells of an endothelial character, with elongated nuclei. The sinus is crowded with 
dividing erythrocytes and with large mononuclear cells, with round, pitted, or notched 
nuclei. Here and there, there is a free polymorphonuclear corpuscle, either with 
hyaline protoplasm or with various degrees of granulation. Within the spaces of the 
trabecular framework are many polymorphonuclear cells, in some cases having all the 
characters of eosinophile leucocytes. 
Further back (fig. 23, Pl. I1.), in the angle between the cardinal vein, aorta, and duct 
‘(text fig. 5), the tissue is not so much opened out, the framework is closer, and in its 
meshes are massed free elements with round, notched, or polymorphic nuclei and various 
degrees of granulation. In the actual blood spaces the great majority of the cells are 
of the large mononuclear variety. 
In the region of the mesonephros the general characters of the tissue round the 
tubules is similar, as will be gathered at once by reference to fig. 26, Pl. III. - 
The individual free cells outside the blood stream vary greatly in size, without any 
further indication of discriminating characters. Mitoses are frequent, but there is 
nothing to indicate that one type of cells is dividing to give origin to another. They 
seem to divide at various stages in the metamorphosis of the nucleus, and all after their 
kind. In fig. 24, Pl. III. there is drawn a cell in one of the venous spaces, which 
from its more crowded nuclear reticulum and the indication of a faint fibrillation of its 
protoplasm is to be regarded as an erythroblast, while outside the blood stream is a 
mononuclear cell of the largest variety, which in general dimensions is equal to the 
erythroblast. 
The cardinal vein, compared with the aorta, contains a disproportionate number of 
white to red elements, and a preponderating number of mononuclear cells. 
Thus in 112 sections the white elements were distributed between the two vessels 
thus :— 
Small Mononuclear. Large Mononuclear. Polymorphonuclear, 
Aorta, 8 He, 8 othe 6 
Cardinal vein, 14 Fon 100 ae 26 
The cardinal vein, however, being much larger than the aorta, it was necessary to 
arrive at the proportion of the white to the red elements in each. This was arrived at 
prop 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART II. (NO. 19). 67 
