DAVIS: SPERMATOGENESIS. 135 
Henking (91) and Montgomery (:01, :06) for Pyrrhocoris and by 
Wilson (:05”) for a variety of Hemiptera. 
A third kind of monosome, one which does not divide in either 
maturation division, has been described by Montgomery (:06) in 
Lygus, an hemipteran. 
B. Diplosomes. 'Vhese are allosomes which are paired in the 
spermatogonia and usually remain compact during the growth period 
of the primary spermatocyte. ‘The diplosomes may be divided into 
three groups. 
1. Diplosomes which typically are unequal in size, but may be 
equal. ‘They may, or may not conjugate temporarily during the early® 
growth period, but always enter the equatorial plate of the first division 
separately and there divide equationally. During the second division 
they divide reductionally, usually after a previous conjugation. ‘These 
are the ‘‘idiochromosomes”’ of Wilson, and have been described in a 
large number of Hemiptera by Wilson (:05* to :06) and Montgomery 
(:06). 
2. Diplosomes, which, as in the first group, are typically unequal 
in size, but may be equal. ‘They conjugate in the primary spermato- 
cytes, usually during the early growth period, but do not separate 
before the first maturation division, where they divide reductionally. 
During the second division they divide equationally. ‘These are the 
heterochromosomes of Miss Stevens; they have been described in a 
large number of Coleoptera by Stevens (:06") and in Coptocycla by 
Nowlin (:06); in the Lepidoptera by Stevens (:06*, Cacaecia, Euvan- 
essa); in the Orthoptera by Montgomery (:05) — this, however, needs 
confirmation; in Forficula by Zweiger (:06); and in arachnids by 
Montgomery (:05, Lycosa). Probably the larger pair of diplosomes 
described by Gross (:04) in Syromastes, as well as those in Tingis 
and Nabis (Montgomery :06), belong to this type. 
3. Diplosomes which are usually much smaller than the other 
chromosomes and form a symmetrical pair in the spermatogonia. 
In most cases they do not conjugate until the prophase of the first 
division, where they divide reductionally. These are the m-chromo- 
somes of Wilson and have been described for a variety of Hemiptera 
by Wilson (:05”), Montgomery (:06) and Stevens (:06°, Aphrophora). 
As Wilson points out, it is doubtful if they have any direct relation 
‘ with the other allosomes. 
Still other types of allosomes have been described in isolated cases, 
but as the accuracy of the results have been questioned, they may for 
our purposes be disregarded. 
