166 Sex- Reversal in Frogs and Toads 



In those cases in which one gonad was a testis and the other an 

 ovo-testis, it is seen that the tissues of the testis are of the formula 

 Sp. 2. This definitely proves that the testis, which contains ovarian 

 pigment and ova, is a gonad in which the transformation from ovary to 

 testis is more advanced than in the gonad of the opposite side. 



Although the process may begin in either gonad apparently, yet in 

 the 18 cases in which anything approaching a true estimate can be 

 made, the right gonad was first affected in 13 cases: the left one in 5 

 only. 



It is the rule that the testis-portion of an ovo-testis is situated upon 

 the inner border of the gland, a position in every way convenient for its 

 association with vasa efferentia. The ovary-portion is always placed ex- 

 ternally to the testis-portion — and this fact has to be remembered when 

 the question as to whether a crest of pigment containing no ovum is 

 ovarian tissue or not is raised. 



It would seem then, that if spermatic tissue becomes developed in a 

 gonad which previously has possessed the characters of an ovary, it 

 makes its appearance in a definite situation. This points to a localisa- 

 tion in the germinal tissue. 



The process thus outlined can be depicted graphically by the use of 

 the formulae employed above. (Ov. 1, it' will be remembered, is ovarian 

 tissue which, on microscopical examination, has the normal structures.) 

 Ov. 1. (Case 1 Rt) 

 Sp. 1, Ov. 1. (Case 1 Lt, and Case 8 both) 



Sp. 2, Ov. 1. (Case 9 Lt ?) 

 I I 



Sp. 1, Ov. 2. (Case 2 Kt, Case 6 both) Sp. 2, Ov. 2. (Case 3 Lt) 



Sp. 1, Ov. 3. (Case 4 Lt, ^Et, 10 both, Sp. 2, Ov. 3. (Case 11 Rt) 

 12 Lt, 14 Lt, 16 Lt, 18 Lt) 



Sp. 1, Ov. 4. (Case 14 Rt) Sp. 2, Ov. 4. (Case 12 Rt, 11 Lt) 



Sp. 2. (Case 16 Rt, 17 Lt, 8 Rt, 19 and 20 both) 



Sp. 1. (Cases 25—32 both) 

 The degenerative changes in the ovarian tissue of both gonads j 

 quickly follow the development of spermatic tissue in one and the degree I 

 of this degeneration is more or less equal on the two sides. There is no 



