SOS The Unity of the Organism. 



A Modicum of Truth in the Mosaic Theory 



It is, then, fully established that in some animals the 

 cells of the early embryos are so specified or individualized 

 that each develops to a considerable extent in its own way, 

 that is, more or less independently of its neighbor cells, 

 and hence may be crudely compared to the stones in a 

 mosaic work — crudely, we must insist, since stones as mem- 

 bers of a mosaic work do not develop at all. 



The Theory of Totipotence 



This theory is the other side of the shield, the side which 

 looks as though the cells of the early embryo are "totipo- 

 tent," that is, as though each cell were able to produce the 

 whole organism instead of only a pre-ordained portion of it. 

 Chieftainship, both experimental and speculative, in this 

 theory of developing embryos is universally accorded to 

 Hans Driesch. The discoveries by him which had such per- 

 vasive influence on biological thinking for more than two 

 decades were first published in 1891. His recent popular 

 account of his work in The Science and Philosophy of the 

 Organism, will best serve our present need. 



Experimental Facts on Which the Theory Rests 



Three years after the publication of Roux's experiments 

 on the frog's egg, above referred to, Driesch tried essen- 

 tially the same experiment, but on a different animal and 

 by a different method. He writes : "It was known from 

 the cytological researches of the brothers Hertwig and 

 Boveri that the eggs of the common sea-urchin Echinus 

 microtuherculatus are able to stand well all sorts of rough 

 treatment, and that, in particular, when broken into pieces 

 by shaking, their fragments will survive and continue to 



