IV. i INITIAL STRUCTURE OF THE GERM 171 



uppermost is retained, then a half-embryo is formed, as is 

 indeed the case, according to Hertwig's own evidence, when the 

 egg is prevented from turning over by compression. 



In such half-embryos Morgan finds no traces of Roux's post- 

 generation, although a whole embryo may be eventually formed 

 by regenerative processes, referred by the author to the retarded 

 development of the living parts of the injured half. It should 

 be noticed, however, that Roux's statements are confirmed by 

 Endres and Walter. 



Should, however, the white pole be uppermost, then a whole 

 embryo of half-size results. In Hertwig's experiments, of course, 

 the original position was usually not retained. 



FIG. 83. Double embryo of Rana fusca, from an egg compressed in 

 the direction of the axis and inverted in the two-cell stage. (After 

 Schultze, from Korschelt and Heider.) 



FIG. 84. Double monsters of Rana fusca, obtained by the same method. 

 (After Schultze, from Korschelt and Heider.) 



This conclusion is still further strengthened by Schultze's 

 observations on the development of eggs inverted in the two- 

 celled stage and kept so. Each blastomere develops independently 

 and a double monster is produced (Figs. 83, 84). The result 

 is not due to the pressure, for controls similarly compressed 

 developed normally. 



The details of development of these eggs have been carefully 

 worked out by Wetzel (Figs. 85, 86). In each inverted blasto- 



