156 FERNANDUS PAYNE. 



the chromosome nncleolus of the growth period (" Karyo- 

 sphere " ) made up of all the chromosomes. 



McGill in her earlier work 'on Aua.r junius ('04) described the 

 accessory chromosome as arising from a union of two small 

 chromosomes as Paulmier had done in the case of Anasa tristis. 

 The later paper of Lefevre and McGill ('08) on the same form, 

 corrects the above error and shows that the accessory chromo- 

 some is a single spermatogonial chromosome. 



The accessory chromosome in the Coleoptera as described by 

 Stevens ('05, '06 and '09) arises from a spermatogonial chromo- 

 some and divides only in one division. 



The idiochromosomes as described by Wilson ('05 and '06) 

 for the Hemiptera, Stevens ('05 and '06) and Nowlin To6) for 

 the Coleoptera, and Stevens ('08) for the Diptera, are two uni- 

 valent spermatogonial chromosomes which usually remain con- 

 densed throughout the growth period. They unite at synapsis in 

 the Coleoptera and one chromosome nucleolus is present during 

 the growth period except in Tcncbrio, where the idiochromosome 

 bivalent does not remain condensed. In the Hemiptera and 

 Diptera they may or may not unite at the primary synapsis to 

 form a bivalent body. In the former case, one chromosome 

 nucleolus is present during the growth period, but separates into 

 its univalent elements before the first maturation division. In 

 the latter case, two chromosome nucleoli are present in the 

 growth period. 



The m-chromosomes as described by Wilson ('05), are two 

 spermatogonial chromosomes which do not unite at the general 

 synaptic period and which may or may not condense in the early 

 growth period to form two small chromosome nucleoli. They 

 undergo a late synapsis in the prophase of the first division to 

 form a bivalent, which divides in both divisions. 



We thus see that the three classes of chromosome nucleoli 

 namely, those derived from the accessory chromosome, from the 

 idiochromosomes, and from the m-chromosomes, are alike in that 

 all are direct descendents of spermatogonial chromosomes. 



The differential chromosomes or chromosome nucleoli of the 

 Reduviidre, which are described in the present paper, are in each 

 case, with the possible exception of Aclwlla ainpliata, univalent, 



