526 Edmund B. Wilson. 



credible, is placed beyond doubt by numerous preparations show- 

 ing every stage in the first division, and no less certainly by the 

 occurrence of two forms of the second division, in equal numbers 

 and appearing side by side in the same cyst, one of which shows 

 seven chromosomes, the other eight, the additional chromosome 

 in the latter case being usually recognizable by its size. Fig. 3, 

 c, d, shows two stages in the history of the heterotropic chromo- 

 some in the first division. Fig. 3, e, /, gives polar views of the 

 two forms of equatorial plates in the second division, one showing 

 seven, the other eight, chromosomes. A large number of sections 

 from different individuals show no exception to this mode of 

 distribution, the two divisions being immediately distinguishable 

 by the size of the cells and by both the size and the form of the 

 chromosomes. A similar case will be described, in Banasa 

 calva, in the following section. 



4. THE CHROMOSOME-GROUP IN BANASA CALVA. 



In this section I shall briefly describe a remarkable form that 

 is unique among the Hemiptera thus far described in that it 

 possesses both the idiochromosomes and a heterotropic chro- 

 mosome; and as a consequence of this it is unique among all 

 described animals in possessing not merely two but four visibly 

 different classes of spermatid-nuclei in equal numbers. These four 

 classes are in no visible way distinguishable in the fully formed 

 spermatozoa, but are clearly apparent in the chromosome- 

 groups of the spermatid-nuclei. 



No spermatogonial metaphase-groups are shown with sufficient 

 clearness to admit of an accurate count, but there are great 

 numbers of dividing spermatocytes which show every stage of 

 both the maturation-divisions. The first division constantly 

 shows, in polar view of the metaphase, fifteen chromosomes, of 

 which two are markedly smaller than the others (Fig. 4, #, ). 

 As is demonstrated by their later history, one of these smaller 

 chromosomes is the small idiochrpmosome (/) and one the heter- 

 otropic chromosome (/?). One of them frequently, but not 

 invariably, lies at one side of the group, sometimes outside the 

 principal ring of chromosomes (Fig. 4, a); but it may lie inside 

 the ring (Fig. I, ). One always lies within the ring; and judging 

 by the analogy of such forms as Lygaeus, Euschistus or Coenus, a 



