510 Edmund B. Wilson. 



small chromosomes, he believed, united in synapsis to form a 

 single condensed bivalent chromosome-nucleolus which persisted 

 throughout the growth-period of the spermatocytes and later gave 

 rise to the small central "tetrad" of the first maturation-mitosis. 

 He believed, further, that after an equal division of this small 

 "tetrad" in the first mitosis each of its products passed undivided 

 to one pole of the second spermatocyte-spindle. He therefore 

 compared the "small tetrad" (microchromosome-bivalent) of 

 Anasa to the body, first discovered by Henking in Pyrrochoris, and 

 afterward found in the Orthoptera and some other insects by 

 McClung and others, to which the last-named author gave the 

 name of "accessory chromosome." In identifying the chro- 

 mosome-nucleolus of the growth-period as the microchromosome- 

 bivalent Paulmier has been followed by Montgomery in all of 

 his papers and with some modifications by Gross ('04) in his recent 

 study of Syromastes. Paulmier's conclusion on this point cannot, 

 however, be sustained, as I shall try to show; and the same is true 

 of his identification of the microchromosome-bivalent as the 

 "accessory" or heterotropic chromosome. 



I. GENERAL HISTORY OF THE M-CHROMOSOMES AND THE HET- 

 EROTROPIC CHROMOSOME DURING THE GROWTH-PERIOD AND 

 IN THE MATURATION-DIVISIONS. 



The behavior of the 777-chromosomes m the maturation-divisions 

 may conveniently be considered first. 



Paulmier's original preparations,^ as well as my own more recent 

 ones, give demonstrative evidence of the equal division of the 

 small central chromosome in both maturation-mitoses, and the 

 same appears no less clearly in Alydus and in Archimerus, pre- 

 cisely as has been shown by Montgomery ('01) in Protenor and 

 by Gross ('04) in Syromastes. I was long since led to suspect an 

 error in Paulmier's conclusion in regard to this point from the 

 fact, which clearly appears in hi&own figures, that the "accessory" 

 is nearly or quite as large as the other chromosomes, and much 

 larger than the products of the first division of the small bivalent. 



'I have in the previous paper acknowledged my indebtedness to Dr. Paulmier's generosity in placing 

 at my disposal his entire series of preparations of Anasa and other insects. He has since added to this 

 indebtedness by sending me from time to time a large amount of valuable living material. 



