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. These 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 pre^ious conjugation. These 

 are the " idiochromosomes " of Wilson, and have been described in a 

 large number of Hemiptera by Wilson {.Qh^ 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 INIontgomery (: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 tj-pes 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. 



