THE MOSAIC STAGE OF DIFFERENTIATION 261 



degrees of diffusion from the regions where they are produced : that 

 in their action at a distance on another developing gonad the 

 inhibitory effect of each is the primary or at least the stronger, 

 and that the male-differentiating substance normally develops 

 earlier and is more potent than the female-differentiating sub- 

 stance. It is also possible that they are or become converted into 

 the sex-hormones of the adult. 



Further highly interesting results have been obtained as the 

 result of fertilising over-ripe eggs in frogs. ^ Below a certain degree 

 of over-ripeness (about 3 days), no effects of any kind are to be 

 noted in the resultant embryos. Beyond this critical point, the 

 following main effects appear, all of them increasing with the degree 

 of over-ripeness. First, a conversion of a certain proportion of 

 genetical females into somatic males. The proportion is at first 

 small, but finally, with eggs rather over 4 days over-ripe, all-male 

 offspring are produced. Meanwhile a certain degree of delay in 

 development is noticeable, and with increasing over-ripeness de- 

 fects of development and abnormal mortality also appear, cul- 

 minating in death of all embryos at an early stage when the eggs 

 are about 5 days over-ripe. The defects of development have 

 already been noted in Chap, v (p. 96); they arise mainly after 

 4-5 days' over-ripeness, and manifest themselves chiefly as a 

 failure of coordination, leading to abnormal cleavage, production of 

 double monsters, development of teratological outgrowths, and in 

 extreme cases the production of abnormal tumour-like structures 

 which partake of many of the characteristics of truly malignant 

 growths. Comparable phenomena have been observed in trout.^ 



The sex-transformations are of peculiar interest, since the whole 

 morphogenesis of the gonad-rudiment is modified. In extreme 

 cases^ the rod-like area of primordial germ-cells does not become 

 detached from the endoderm, and the gonad-rudiment at its first 

 appearance is a rudimentary fold containing no germ-cells (in such 

 cases the germ-cells appear later to migrate into it, but how this 

 occurs is not established). In other cases'* the germ-cells while still 

 in the endoderm become abnormally pigmented. The gonad- 

 rudiment in highly affected specimens passes through a female 



^ Willier, 1932; Witschi, 1932. " Mrsic, 1923, 1930- 



3 Kuschakewitsch, 19 10. * Witschi, loc. cit. 



