252 Proceedings of the Royal Physical Society. 
gonads are grades of a single process. Synchronously, or in succession, 
upon the inner border of one or both gonads which previously had presented 
characters entirely ovarian and which, in some cases evidently, had attained 
functional maturity, one or more nodules of spermatic material made their 
appearance. Very shortly following the expression of the spermatic tissue, 
the ovarian tissues of both gonads began to degenerate and to become 
removed, whilst their further production became inhibited, whereas the 
spermatic progressively increased in amount and functional powers. Soon © 
the gonads are as the right gonad in Fig. 7, and then as those in Fig. 11, 
irregular in shape, partly ovarian and partly spermatic, having the 
appearance of abnormal testes bearing pigment along the outer border. 
The irregularity of shape and the surface scarring result from the inter- 
ference with the even growth of the active spermatic tissues which follows 
from the presence of what must be considered as foreign bodies, the pigment 
and fibrous tissues of the degenerating ovary. Then the gonad will become 
as the right one in Figs. 16 and 19, a normal testis, save that a small quantity 
of polygonal masses of pigment and slight scarring still remain upon the 
outer border. But scars heal and foreign matter is ultimately removed, and 
later the gonad will assume the form of a normal testis. A gonad which 
previously had every character of a perfect ovary, has thus become replaced 
by a perfect testis. 
An ovum is seen lying amid the spermatic tissues between the seminal 
tubules, in Fig. 14, and within a tubule in Figs. 3 and 17. The tubules 
in the neighbourhood are contorted. In the case of the juvenile testis of 
the frog, the origin of the large cells closely resembling ova, which are 
sometimes found therein, may be a debatable question, but there is no doubt 
as to the origin of the ova as seen in this case. There is no reason to 
suggest that such cells have been produced by the spermatic tissues, for 
it is seen that the surface of the degenerating ovarian tissues are in 
intimate contact with the actively growing testis-portion of such a gonad, 
so that an ovum, a product of the ovary-portion, becoming extruded from the 
surface thereof, may readily become surrounded and included by enveloping 
spermatic tissue, and there remain among the connective tissue, between the 
seminal tubules, or actually within a seminal tubule, secure from the action of 
whatever is responsible for the rapid degeneration of the ovarian tissue 
generally (Figs. 6 and 8a). Such ova, therefore, may become the sole — 
remains of ovarian tissues in a gonad which in every other respect is a perfect 
testis. Ultimately these ova must become fesorbed, and the gonad thus 
becomes a perfectly normal testis. The pigment in Figs. 20 and 21 is a 
similar inclusion. ¢ oa 
