304 EDMUND B. WILSON. 



meet this difficulty or to give an adequate explanation of the facts ; 

 and for a time, I even suspected that the material might be path- 

 ological. Recently, however, I have found a similar, though not 

 quite identical, condition in a species of Metapodius, and have been 

 able to study the facts more thoroughly. In this form, too, an 

 unpaired chromosome coexists with a typical pair of idiochromo- 

 somes (and a pair of ///-chromosomes as well ) ; but the facts 

 clearly show that it is not of the same nature as the " accessory " 

 or " heterotropic " chromosome of the usual type, and is with- 

 out constant relation to sex-production. The idiochromosomes 

 show the usual relation, the large one passing to the female pro- 

 ducing pole and the small one to the male-producing pole. A 

 comparison of different individuals shows beyond doubt that the 

 unpaired chromosome may be either present or absent in either 

 the male or female, and hence is without significance in sex- 

 production. It is in fact a kind of supernumerary chromosome, 

 which I shall designate as the "^-chromosome " in order to dis- 

 tinguish it from the odd sex-chromosome of the usual type - 

 variously known as the " accessory chromosome " (McClung), 

 " heterotropic chromosome ' (Wilson), or " monosome ' 

 (Montgomery). 



i. METAPODIUS TERMINALIS Ball. 1 



The present account will give only the facts that bear directly 

 on the case of Banasa calva. The genus Metapodius is, I believe, 



1 The following description will be found to differ widely from that given for the 

 same species by Montgomery (Trans. Am. Phil. Soc., N. S., XXI., 3, 1906), who 

 states that there are 21 spermatogonial chromosomes and an ordinary large odd 

 chromosome in the second division. Professor Montgomery has kindly sent me some 

 of his own material, collected in Pennsylvania, a study of which has convinced me 

 of the correctness of his account. My own material is from New Jersey, North Caro- 

 lina, South Carolina, Georgia and Ohio ; and there can be no doubt of the identifi- 

 cation since every original specimen is in my possession (as is the case with all my 

 new material). Through the courtesy of Dr. Uhler I have been enabled to compare 

 these specimens with those in his collection (with which they exactly agree) ; and 

 they have also been examined by several competent hemipterists, including Mr. Otto 

 Heidemann, of Washington, and Mr. H. G. Barber, of New York, and pronounced 

 by them to be typical terminalis. As will be shown, different individuals among 

 these specimens show constant and characteristic differences in the chromosome- 

 groups ; but none show less than 22 chromosomes, and none possess a large odd 

 chromosome. The same is true of M. femoratus Fab., and M. granulosus Ball. , both 

 of which, like terminalis, possess a typical pair of idiochromosomes. This contradic- 



