A Comparative Study of thc Chromosomes etc. 
243 
II. Synopsis of Previous Papers on the Chromosomes in Hemiptera. 
The literature on the spermatogenesis of the Homoptera (Hemiptera 
homoptera) may be saicl to begin with the study of Cicada tibicen by 
WiLcox (’95). His material consisted of only three specimens, which 
did not Show division stages. He States, however, that the spermatogonia 
contain 12 chromosomes, and the sperniatocytes of the first Order 24 sphe- 
roidal bodies and one or two nucleoli. From his figures or account, we 
gain 110 evidence for or against the presence of “sex-chi’omosomes” in 
this insect. Ten years later Stevens (’Oöa, ’Oöb) described the sperniato- 
genesis and oögenesis of a niiraber of aphids. Both spermatogonia and 
oögonia were described as having the same (even) number of chromo- 
somes in a given species, and therefore no “ A'-chromosonie” in the male, 
althoiigh one chromosome was described as lagging in the anaphase of 
the first spermatocyte division (’Oöb, Figs. 217—218). Later, however, 
when the works of Morgan and of von Baehr on the aphids and phyl- 
loxerans had appeai’ed, she (Stevens, ’09b) reexamined her material 
and showed that this lagging chi’omosome was in reality an ‘LY-elenient”, 
and that the male possessed an odd number of chromosomes in the 
spermatogonia. Both Morgan (’08, ’09) and von Baehr (’09) have 
shown that the males of Äphis, Phylloxera, and Pemphigus have a de- 
finite “A'-elenient”, which in certain cases, as in Phylloxera caryaecaulis, 
may be represented by two clu’omosomes, and that this “X-element” 
passes to that one of the two secondary spermatocytes which finally 
gives rise to two functional spermatozoa, while the otlier secondary 
spermatocyte, lacking the “X-elenient”, degenerates. The male is pro- 
duced parthenogeneticaUy from an egg which reduces its “X-chromatin” 
through maturation to one half that of the female sonia. In turn, since 
only feniales are produced from fertilized eggs, only “female determining” 
spermatozoa, those with an “X-element”, iiiature. 
Stevens (’06) also described the spermatogenesis of Aphrophora 
quadrangularis, one of the Cercopidae, a family not distantly related to 
the Membracidae. This form agrees closely with E. curvata in the be- 
havior of its chromosomes. It possesses a single “X-element”, which, 
like that of most of the Orthoptera, passes undivided to one of the se- 
condary spermatocytes. She also figured a pair of very large cm'ved 
chromosomes 3) and a pair of small “m”- or micro- chromosomes. 
3) A similar pair of large chromosomes occurs in E. curvata and E. Unotata, as 
well as in several other Homoptera. I shall refer to them as the macro-chromosomes, 
or “J/-chromosomes-’. 
