IV. i INITIAL STRUCTURE OF THE GERM 



201 



theless capable of total development in a very marked degree. This 

 capacity is not, however, unlimited, but diminishes as develop- 

 ment proceeds, and it appears highly probable, and is indeed 

 often admitted by Driesch, that the chief cause of this restriction 

 is the lack of some specific substance and not the deficiency of 

 mere material, though this may be a subsidiary factor. The 

 progressive loss of potentialities is exhibited also by the embryonic 

 organs as they are formed later on. 



a 



b. 



c. 



FIG. 112. Echinus, the tripartite gut of the complete Pluteus : 

 o. }, b. I, c. J. (After Driesch, 1900.) 



Before concluding this section we must notice an experiment 

 which is the converse of those considered above, namely, the 

 production of one embryo from two eggs. 



An unsuccessful attempt was made by Morgan to obtain this 

 result. This author only succeeded in showing that the eggs of 

 SpJiaercchinns, when deprived of their membranes by being 

 shaken, tend to fuse together, and that from such pairs double 

 monsters may be produced with two guts and two skeletons. One 

 skeleton may, however, very largely predominate over the other, 

 which indeed remains rudimentary, and the guts may coalesce. 



