Vol. XVI. March, /pop. No. 4. 



BIOLOGICAL BULLETIN 



SOME NEW TYPES OF CHROMOSOME DISTRIBU- 

 TION AND THEIR RELATION TO SEX. Continued. 



FERNANDUS PAYNE. 



GENERAL. 

 The Chromosome Nucleoli. 



The term " chromosome nucleolus " has come to mean, in a 

 general sense, any chromosome, which remains condensed during 

 the growth period. Under this heading, then, I shall discuss 

 briefly the origin, valence and history of four different classes of 

 chromosomes, namely : the accessory chromosome, idiochromo- 

 somes, m-chromosome and differential chromosomes. 



Henking ('91) observed a deeply staining body in the growth 

 period of the primary spermatocytes of Pyrrhocoris, but did not 

 detect its origin. He did recognize its chromatic nature and its 

 unequal distribution in the second division, whereby one sperma- 

 tozoon received one more chrjomatin element than the other. 

 Montgomery ('98) was the first to detect that the accessory chro- 

 mosome (chromosome nucleolus) was nothing more than a 

 spermatogonial chromosome which differs in its behavior from 

 the others, but he believed that it divided in both divisions. 

 Paulmier, in his work on Anasa tristis ('99) described an acces- 

 sory chromosome or what he called a " chromatin-nucleolus," 

 which he thought originated at the time of synapsis by the union 

 of two small spermatogonial chromosomes, divided in the first 

 maturation division, but passed over undivided in the second. 

 Montgomery ('01) discarded his former interpretation ana ac- 

 cepted that of Paulmier. In the case of Syromastes ('04) and 

 Pyrrhocoris ("06), Gross believed the accessory chromosome to 

 arise by the fusion of two spermatogonial chromosomes which 



