356 The Histogenesis of the Adrenal in the Pig 
to the coelomic epithelium has increased to such an extent that it is 
extremely difficult to define any boundary between the two structures 
(Fig. 4); and the difficulty is not lessened by attempts to draw distine- 
tions between the cells composing them. Mitoses are frequent both in 
the anlage and in the epithelium. The furrow previously mentioned is 
still present, but the anlage les against the lateral wall of the furrow 
rather than at its bottom. Asa result of these findings, it was somewhat 
confidently expected that younger embryos would reveal an invagination 
of the coelomic epithelium such as Aichel found in the rabbit; but such 
was not the case. In embryos of 7 and 6 mm. no evidence of the anlage 
could be found, except, possibly, a suggestion of thickening at the usual 
situation. In the hope of finding something more definite, six embryos 
varying from 8 to 6 mm. were sectioned, but none of them furnished 
any additional light. 
It is clear that one would not be justified in drawing positive con- 
clusions from these findings; but such testimony as they bear would 
seem to be on the side of those who hold that there is a genetic relation 
between the coelomic epithelium and the adrenal cortex. One may 
suppose that the anlage is laid down by invaginations occurring suddenly 
and hence missed in the embryos sectioned, or by epithelial cells wan- 
dering into the mesenchyme. In the latter case, however, we should 
still have to decide whether the cell-wandering is sufficiently direct and 
great to constitute a distinctly special process in this region. 
THe HISTOGENESIS OF THE MEDULLA. 
My observations are entirely in accord with the conclusion of Flint," 
that the medulla of the adrenal is developed from certain small cells 
found in the pig of 35 mm. at the periphery of the cortex just within 
the capsule. He seems to have shown beyond a doubt that these cells 
are the ancestors in direct line of the mature medullary cells. The 
problem left, therefore, is to trace these cells to their source. The re- 
sults of the present study point to the sympathetic ganglia as that 
source. 
Tracing the relationship between the adrenal and the sympathetic 
ganglia in the course of their development, we find that in the pig of 
13 mm. the ganglia are quite small. They lie dorso-lateral from the 
aorta nearly opposite to the dorsal border of the Wolffian body, and are 
connected with the spinal nerves by the splanchnopleural branches. 
Smaller collections of ganglion cells with many mitotic figures can be 
13 Op. Cit. 
