Studies on Chromosomes. 521 



however, conclusive evidence that such is not the case. In this 

 stage (corresponding to-Paulmier's Figs. 22, 23) the chromosome- 

 nucleolus is still unmistakably recognizable by its compact and 

 rounded appearance, while the other chromosomes, including the 

 two microchromosomes are still in the form of paler and more 

 diffuse bodies. The m-chromosomes at this period (one of 

 them is clearly shown in Paulmier's Fig. 24) appear as short, 

 more or less ragged, paler, irregular rods that give the appearance 

 of being longitudinally split (Fig. 2, b-d). Some of the cysts 

 at this period show every stage in the condensation of these two 

 small diffused chromosomes to form the two small, dyad-like micro- 

 chromosomes that conjugate to form the small central bivalent. 

 1 have studied numerous nuclei in these stages with great care, 

 and believe that they remove every doubt that the two micro- 

 chromosomes that conjugate to form the small central bivalent in 

 Anasa arise neither from separate small condensed bodies, as in 

 Protenor or often in Alydus, nor from the single large chromosome- 

 nucleolus as assumed by Paulmier, Montgomery and Gross, but 

 from diffused masses similar to the larger ordinary chromosomes 

 during the greater part of the growth- period. The same fact may 

 be seen in Chariesterus, though I have not in this case so complete 

 a series of stages. The chromosome-nucleolus must therefore 

 give rise to one of the larger chromosomes; and the exact agreement 

 of Anasa with Alydus and Archimerus, save in the one point of 

 the later condensation of the microchromosomes in the former 

 form, justifies the confident conclusion that in Anasa the chro- 

 mosome-nucleolus IS the ^^ accessory'' or heterotropic chromosome. 

 Anasa, Alydus, Chariesterus, and Archimerus thus fall in line 

 with the facts observed in the Orthoptera, and I believe the same 

 will prove to be the case with other Hemiptera in which an "odd," 

 "accessory" or heterotropic chromosome occurs.^ This result, 

 which is wholly at variance with the accounts of previous 

 observers, forms the first step in clearing away the confusion 

 that has hitherto stood in the way of a consistent general inter- 

 pretaticn of the heterotropic chromosome. 



*I cannot at present offer a definite explanation of the divergence between this result and that reached 

 by Gross in Syromastes. Without questioning the accuracy of his figures, I feel confident, in view of 

 what I have seen in so many other forms, that further examination of this genus will give a different 

 result, both on this point and on a number of others. 



