30 Papers from the Marine Biological Laboratory at Tortngas. 



division separating whole chromosomes which had united to form bivalents 

 in synapsis. This division results in dimorphic secondary spennatocytes, 

 one group possessing, the other lacking, the accessory chromosome. 



(g) The second maturation division is equational, effecting a longitu- 

 dinal division of univalent chromosomes. The accessory also divides equa- 

 tionally in the cells containing this element and lags somewhat behind the 

 ordinary chromosomes. 



(h) A dimorphism of spermatozoa results ; the accessory chromosome 

 possessed by one-half probably represents a sex-determinant. 



(/) Nothing appears in the phenomena of synapsis or reduction as re- 

 gards the ordinary chromosomes to suggest anything contradictory to the 

 theory that synapsis signifies the final phase of fertilization and the union 

 of maternal and paternal chromosomes, nor yet to contravene the theory 

 of the individuality of the chromosomes ; but no clear evidence appears in 

 support of either hypothesis. 



(/) The history of the accessory chromosome gives evidence that it at 

 least possesses a strict morphological and probably also a physiological 

 individuality. 



