242 
Sidncv I. Koriihauser 
Page 
X. Discussion 274 
A. Syndesis and tlie matnration divlsions 274 
B. The sex-chromosomes 279 
XL Summary 286 
Bibliography 287 
Explanation of plates 293 
I. Introduction. 
The work on tliis paper was done at the Zoölogical Laboratory of 
Harvard University during the years 1909 to 1912, and at the Biological 
Laboratory of the Brooklyn Institute at Gold Spring Harbor, Long Island, 
during tlio sunimers of 1908, 1910, and 1911. I am especiaUy indebted 
to Professor E. L. Mark of Harvard University for his guidance and 
advice in directing my work, and to Dr. C. B. Davenport, of Gold Spring 
Harbor, for his many valuable suggestions and aid, which permitted 
me to obtain and study an abundance of material during three summers. 
I also wish to express to thosc who aided me in procuring material 
appreciation of theü' Services, likewise to ]\Ir. Ignaz ÄIatausch, Pro- 
fessor E. D. Ball and JHr. G. W. Johnson for the loan of speciniens, 
and to jVIr. E. P. Van Puzee, Professor E. D. Ball and Professor 
Herbert Osborn for their opinions regarding the systematic relation 
of the species considered. 
The paper is an attempt to foUow in some detail and in a comparative 
manner the behavior of the chromosomes in the spermatogenesis of two 
nearly related membracids, Enchenopa hinotata (Say) and Enchenopa 
(Campylenchia^) curvata (Fahr.). The insects in question not only bear 
a niarked resemblance to each other externally (Plate XVIII, Fig. 1 and 2), 
but the general make-up of their chromosomal complexes is quite similar 
(Plate XIX, Figs. 15, 18, 20—28 and Plate XIX, Figs. 33—38); however, 
there is this one marked difference, E. curvata has a definite and well 
mai'ked unpaired “X-chromosome”^); E. Unotata has no such unpaked 
chromosome. 
1) As there is some question whether or not Campylenchia {Stä\) is a well founded 
subgenus of Enchenopa, I shall consider “binotaia” and ''curvala” as members of the 
genus Enchenopa Am. et Serv. A discussion of this question follows in the text. 
2) “X-cliromosome” or “X-element” refers to the unpaired chromosome found 
first in Pijrrhocoris by Hexkixg (’91) in his study of the spermatogenesis of that 
insect and designated by the letter “X” in his figures. It was later called the “acces- 
sory cliromosome” by McClung, the “heterotropic chromosome” by Wilson, and 
the “monosome” by Moxtgomery. 
