262 



THE MOSAIC STAGE OF DIFFERENTIATION 



phase followed by degeneration of the cortex and growth of the 

 medulla leading to male transformation as in the high temperature 

 experiments: in extreme cases, the cortex is inhibited from the 

 outset and sexual diiferentiation is male throughout. In general, 



Fig. 125 

 The effect of late fertilisation on gonad-differentiation in frogs. Left, two stages 

 in the normal morphogenesis of the gonad. Above, genital ridge with primordial 

 germ-cells and mesenchyme. Below, later stage with peripheral cortex containing 

 primordial germ-cells and central medulla derived from the invading rete-cords 

 of nephrogenous origin. Right, corresponding stages in embryos from late 

 fertilised (over-ripe) eggs. Above, very small genital ridge with no primordial 

 germ-cells . Below, later stage with invading medulla (rete tissue) but rudimentary 

 cortex, with no primordial germ-cells. (Redrawn after Kuschakewitsch, 

 Festschr.f. R. Hertwig, 1910, vol. ii.) 



testis- differentiation is accelerated^ (fig. 125). The thyroid of late- 

 fertilised frogs is also hypertrophied.^ 



We have thus a series of effects with progressive degrees of 

 over-ripeness. First, minor upsets of morphogenesis, notably in 

 regard to sex. Secondly, more general upsets of morphogenesis, 



^ Eidmann, 1922. 



- Adler, 1917. 



