[macallum] SEMI-CENTENNIAL OF THE ORIGIN OF SPECIES 187 



chromatin in the female pronucleus to form the first nucleus of the new 

 organism. All this postulates that the chromatin is the bearer of the 

 qualities of heredity, in other words, that it is the material which directs 

 all the course of development of the offspring. Further, it is commonly 

 assumed that the chromatin in the nucleus has been formed there out of 

 simpler material reaching it from the surrounding cytoplasm, or ulti- 

 mately from tlie circulatory fluid in a metazoon or metaphytan form. 



If this latter assumption is well founded then Weismann's germ- 

 plasm may exist, indeed, must exist, for if the nucleus manufactures its 

 own chromatin the processes involved must rarely if ever vary, and con- 

 sequently the product, the heredity-bearing material, must be persistent 

 in its composition. 



The cardinal point then is does the nucleus form its own chromatin 

 or is it derived from without? 



On this point we have little evidence, but such as it is it is of value. 

 Iwanoff 1 has shown in the case of the yeast organism that the cytoplasm 

 contains a ferment which converts phosphoric, acid and sugar into a 

 ccmpound in which the acid is masked as it is nucleic acid. This com- 

 pound is, in all probabilit}^ the skeleton component of chromatin. 

 PopoflF^ has recently demonstrated that in Protozoa, when a portion of 

 the cytoplasm is cut away, the chromatin of the nucleus is less readily 

 replenished than in the intact cell. 



There are also the observations which I made seventeen years ago 

 on larval Amblystoma. In these as in all the lower vertebrates the 

 vitellin of the yolk spherules contains iron and phosphorus and is the 

 source of the iron and phosphorus of the chromatin. N"ow in the de- 

 veloping larva the vitellin dissolves in the cells, and some of it at least 

 diffuses from them into the blood plasma. The latter at a certain stage 

 of development gives in sections of the embryo distinct evidence of the 

 presence of a " masked " iron chromatin-like compound which takes the 

 staining dyes readily. At a later stage this diminishes and almost dis- 

 appears from the blood plasma. The embryonic red cells, before this 

 diminution takes place, manifest an extraordinary activity in division, 

 so much so that each for a time seems to have no resting phase. This, 

 I have explained is due to the richness of the plasma in a chromatin- 

 like material which diffuses into, or is absorbed by, the embryonic red 

 cells, and thus their chromatin is so abundant as to permit many divi- 

 sions immediately following each other. 



The evidence then as far as it goes seems to indicate that chromatin 

 is not wholly formed in the nucleus in which it is found. If it is derived 



1 Zeit fur Physiol. Chem., Vol. 50, p. 281, 1907. 



2 Arch, fiir Zellforschung, Vol. I, p. 245, 1908. 



