76 ETHEL NICHOLSON BROWNE 



Here the accessory becomes attached to another chromosome in 

 th first division, and goes over with it to one pole. McClung 

 ('05) describes a similar relation for the acridian Hesperotettix 

 and the locustid Anabrus. In Hesperotettix he found that it 

 is always the largest chromosome with which the accessory is 

 associated. In Mermeria, another acridian, a similar multiple 

 element becomes further associated with another tetrad, and in 

 division this complex acts as a single bivalent, with the anoma- 

 lous result that entire tetrads pass to one pole. More recently. 

 Boring ('09), Boveri ('09) and Edwards ('10) have found in the 

 case of Ascaris megalocephala that the accessory may be free or 

 may be indistinguishably united with another chromosome. 

 Stevens ('11) similarly finds in one of the mosquitoes a close 

 union of X and Y with a pair of autosomes in the spermatocyte 

 di\'isions, while in the spermatogonia they may or may not be 

 closely united with them. 



In a third category we may place the form N. insulata where 

 there is a temporary association and separation of two ordinary 

 chromosomes (autosomes). That this association has some sig- 

 nificance can scarcely be doubted when we consider that it is 

 always two particular chromosomes that are united. If the 

 union of the two chromosomes is the primitive condition, then the 

 secondary separation might mean that certain characters are 

 being segregated from other characters. If the separation 

 is primary, the fusion of the chromosomes might mean that a 

 certain series of characters which were entirely independent of 

 another series have become linked with them. It is possible that 

 just as the association of a sex-chromosome and an autosome may 

 serve as a morphological basis for sex-linked inheritance as pointed 

 out by Wilson ('11), the association of two autosomes may give 

 the morphological basis for the cases of coupling that have 

 recently been made known in experimental work. For example, 

 Bateson and Punnett ('11) find that in the sweet pea, blue color 

 and long pollen are usually combined, red color and round pollen, 

 etc.; and in Primula, according to Gregory ('11), magenta color 

 is coupled with short style. In Drosophila also, a linkage of 

 a color and a wing factor has been found by Morgan and Lynch 



