38 



curs when the spores are formed, which may be many thousands of cell 

 generations remo^■e<l from the time in ontogeny when eggs and sperms are 

 differentiated; while in animals the reducti<m immediately precedes the 

 formation of the gametes. In regard to the chromosomes themselves, the 

 view generally prevailing is that each possess a distinct identity or indi- 

 viduality which is maintained throughout ontogeny, and phenomena per- 

 taining thereto have been presented under the theory of the individuality 

 of-the chromosomes. Very recently, however, the idea of individuality has 

 been taken away from the chromosomes and applied to smaller units, such 

 as the eliromonu'res. or better the microscoi)ical]y distinguishable granules 

 which make ui« tlie chromomeres. We m;iy call tht'se particles pangens, 

 or select any name which may be convenient and likely of adoption. The 

 writer has expi'essed liis views on this subject in greater detail in a recent 

 publication, and only a few brief statements will be made here, in as much 

 as a fuller discussion is regarded as being too technical for a general audi- 

 ence. The idea of individuality is apjilied to the chromomeres or the small 

 particles comi)Osing them, chielly because tlie identity of the chromosome 

 is lost in the i-estin nucleus. 'There are no good reasons to believe that 

 a given chromosome always contains the same hereditary qualities in any 

 succession of cell generations. Furthermore, no special importance should 

 be attached to the different si5:GS of the chromosomes, for, as a rule, one 

 of the most striking jihenomena in a dividing nucleus is the marked differ- 

 ence in the size v.f the chromosonn'S. These small material particles, or 

 pangens, are responsible for the characters of the individual, although they 

 are not regarded as tlie immediate characters themselves. They may be 

 roughly compared with ferments, bringing about changes which collectively 

 constitute development, and produce those <-heiiiicaI re-arrangements of 

 which form, color, and so forth, are the visible expression. Fused gamete 

 nuclei, however, do not constitute a chemical union but a mechanical mix- 

 ture. The numerical reduction of the chromosomes is a consequence and 

 a condition of sexuality. It is probably not a mere halving of the bulk of 

 the chromatin, but a selection and a distribution between daughter cells of 

 structural entities— the primordia of characters which are handed from 

 one generation to another. The Mendeliaii jirinciple shows, if it shows 

 anything worth while, that these units ai-t independently. The nucleus, 

 therefore, directs and controls cellular de\elopiiient. The outer manifesta- 

 tions known as variation are probably due to the inter action of nucleus 

 and cytei)lasm. 



