12 MONTGOMERY— CELLULAR BASIS OF HEREDITY. [Jan. 15, 



But how account for the preliminary pairing of the chromo- 

 somes ? It is apparent that each spermatozoon may be called 

 paternal, but not male, and each egg cell maternal, but not female, 

 for the following reason : We have seen that each organism formed 

 by fertilization has a fixed number of chromosomes, half of which 

 were derived from the spermatozoon and half from the egg cell. 

 The germ cells that develop within that organism, be they sperma- 

 tozoa or egg cells, accordingly have an equal number of chromo- 

 somes from each parent. Therefore, the spermatozoon contains 

 maternal as well as paternal chromosomes, and the egg cell pater- 

 nal as well as maternal chromosomes. And, therefore, each germ 

 cell has in equal measure the hereditary substance of both its 

 parents. 



Now the process of pairing of the chromosomes, which we found 

 to be an initial step to their reduction in number, has been proved 

 to be a pairing of paternal with maternal chromosomes (Mont- 

 gomery, A Study of the Chromosomes of the Germ Cells cf the 

 Metazoa, 1901). In a particular generation of the sperm cell it 

 was demonstrated (and not merely '' surmised," as stated by another 

 worker) that paternal chromosomes pair with maternal ones, form- 

 ing thus double rods instead of single ones ; it is probable, but not 

 yet demonstrated, that likewise in each egg cell, of the correspond- 

 ing generation, paternal chromosomes pair with maternal. Thus 

 in the reduction division, which displaces the two elements of a 

 pair, a maternal chromosome separates from a paternal in each 

 pair, but not so that all the paternal chromosomes pass into one 

 cell and all the maternal into another. 



These facts which we have learned about the chromatin! lead to 

 a conclusion that for its probability approaches a fact. That is, 

 that the different chromosomes in a germ cell have each their par- 

 ticular values. Roux {Ueber die Bedentung der Keriitheihmgs- 

 figuren, 1883) was the first to postulate that the chromatin cannot 

 be hereditarily the same throughout the length of a chromosome, for 

 otherwise its equal longitudinal splitting would be without mean- 

 ing. In other words, each particular portion of a chromosome 

 would represent a particular hereditary value. Not only is this 

 probable, but it is also probable that one chromosome has heredi- 

 tary values not found in the others. For we have seen that each 

 germ cell has a set of maternal and a set of paternal chromosomes, and 

 that in a particular generation those of the one set pair with those 



