ABSTRACT
In frog tadpoles the interrenal blastema proliferates from the lateral plates in the zone where the splanchnopleures meet to form the dorsal mesentery. At first the interrenal proliferation appears distinct and separate from the mesonephric blastemata which, in the form of nephrogenic cords, occupy a more lateral site. In later stages the interrenal blastema moves dorsally from its site of origin to join secondarily, under the aorta, the medial faces of the mesonephric blastemata, which are now differentiating their tubular structures.
The interrenal blastema in early stages contracts relationships with the primordial germ-cells, when the latter form a median unpaired genital ridge at the mesenteric root; and it provides these cells with the first somatic follicular elements, which will then take part in the genesis of the gonadal cortex. A further participation of the interrenal blastema in the constitution of the gonadal cortex is also observed later, at the stage when paired genital ridges lie one at each side of the dorsal mesentery. In this stage interrenal cells descend towards the gonadal primordia, moving down along the walls of the vena cava, and penetrate between the germ-cells, contributing further to the formation of their follicles. The interrenal blastema later continues to penetrate into the gonadal rudiment, now providing only medullary tissue.
Such embryological relationships between the interrenal blastema and the somatic cortical and medullary tissues of the gonads suggest the following points.
(a) They appear to be in accord with the chemical and physiological likeness of the steroid hormones which will be secreted by these tissues in the adult.
(b) They further suggest that sex differentiation of the Amphibian gonads is not based on a predetermined antagonism between a cortical and a medullary somatic tissue, each different from the beginning both in activity and in embryonic origin. On the contrary, the common embryological derivation of these territories agrees very well with their reported power of partly modulating themselves in either an ovarian or a testicular direction, according to the gonadal sex differentiation. The feminizing potentiality of the cortex on the one hand, and the masculinizing potentiality of the medulla on the other hand, seem thus to establish themselves little by little, during the process of gonad differentiation, under the activity of the genetical factors of sex determination.
Analogous powers of transforming their morphogenetic destinies seem also to have already been reported, by other workers, for the cells lying in the boundary zone between the interrenal and the mesonephric blastemata. All the blastemata of the urogenital area, which have a mesodermal origin, seem therefore to be endowed with a certain degree of pluripotentiality, their definitive morphogenetical determination being gradually attained in the course of development.