220 DARWINISM TO-DAY. 



is formed at first in scattered bits in the nutritive plasm mass, but 

 as these bits increase they join and become united into a network 

 surrounded by and containing in its meshes the nutritive plasm. 

 And one of the most interesting parts of Nageli's hypothesis is that 

 he conceives this network of idioplasm not to be limited by cell 

 boundaries but to penetrate from one cell into adjacent cells and 

 thus to spread through and unite in a most significant and important 

 way all the cells and tissues of the body. It is just this sort 

 of a ramifying, stimulus-carrying, protoplasmic network connect- 

 ing all the parts of the body that the believers in the inheritance 

 of acquired characters seem to need as a mechanism to transmit 

 from soma to germ-cells the effects of external and functional 

 stimuli. 



Next, the theory of intra-cellular pangenesis of de Vries may 

 be briefly stated. This theory has become the more important be- 

 cause of the great interest aroused by and the large appreciation 

 given to the mutations theory of species-forming of the same 

 biologist. De Vries's theory of intra-cellular pangenesis has much 

 in common with Darwin's theory of the pangenesis of gemmules, 

 but it is able to do away with that particularly weak part of Dar- 

 win's theory, which postulated the circulation of the gemmules 

 throughout the organism in order that the^^hould meet in the 

 germ-cells and modify these cells in a paraH^^^y with the modi- 

 fications occurring in the peripheral organs. ^IB n na d to postu- 

 late this circulation of the gemmules through the^fcganism in order 

 to explain the phenomena of regeneration, and fhe heredity of 

 acquired characters. Now that the heredity of acquireVcharacters 

 has been shown to be at best an extremely doubtful phenomenon, 

 and that regeneration is explicable by other means, de Vries has 

 been able to drop this weakest part of the Darwinian conception. 

 So that in the theory of the later biologist, the circulation of gem- 

 mules does not extend from one cell to another throughout the 

 body of the organism, but limits itself to that particular cell in 

 which it is created and circulates only between the nucleus and 

 cytoplasm, from which comes the name, "intra-cellular pangenesis," 

 as distinguished from Darwinian pangenesis. De Vries' theory may 

 be abstracted as follows (following Delage) : 



The form and properties of cells result from their protoplasmic 

 composition just as the properties of the inorganic bodies result 

 De Vries's from their chemical composition. Is it necessary, then, 

 theory, to admit that there are as many kinds of protoplasm as 



there are different sorts of cells in the organised beings? When one 

 recalls how many different cells there are in a single organism, and 

 that the homologous cells are not identical in different species, one 



