CHROMOSOMES IN THE SPERMATOGENESIS OF THE IIEMIl'TERA HETEROTTERA. 139 



of tlie second ; a large and small diplosome [di. 1, Di. 1) that divide separately and 

 therefore equationally in the first mitosis, but conjugate in the second spermatocytes 

 and undergo a reductional separation there ; and a small bivalent element, Di. 2, di. 2, 

 that may be another diplosome, Avhich divides in both mitoses as do the 15 autosomes. 

 (Consequently each spermatid must receive Jialves of the 15 autosomes and of the ele- 

 ment dL 2, di. 2, half of them receive Di. 1 and the other half receive (//. 1, and half 

 of them get the monosome. 



From these relations wc may conclude for the spermatogonium: 30 autosomes, 

 one monosome, one large and one small diplosome [di. 1, I>i. i), and a pair of small 

 diplosomes {J)l. 2, di. 2), a total of 35 elements. 



Literature. — In my earlier account I overlooked the small monosome, and did 

 not describe the second maturation division. 



II. General Considerations. 

 1. Behavior and Significance of the Allosomes. 



In the Hemiptera heteroptera the alloson^es present the following relations in the 

 spermatogenesis : 



A. Only Diplosomes Present, and these exhibiting the following differences : 



Al. The diplosomes conjugate early in the growth period, divide reductionally 

 in the first maturation mitosis, and equationally in the second. This is the case in 

 TiiKjis, where there is a single pair with components of very unequal volume ; and in 

 AcJiolla (4 pairs) and Si'iiea (3 pairs), where the diplosomes are very small and the 

 components of a pair of about equal volume. In tSineu and Acholla they remain dense 

 during the growth period ; in Timjis it was not determined how they behave during 

 this stage. 



A2. One pair of diplosomes Avhich divide separately and equationally in the first 

 maturation mitosis, but in the second spermatocytes conjugate and then divide reduc- 

 tionally. This modus was first discovered by Wilson ; I had shown (1901?>) that in 

 certain species {Euschistus tristigmus, Oncopeltus, Zaitha) the diplosomes divide separ- 

 ately in the first maturation mitosis, but I failed to note, because in these species I 

 omitted to describe the second mitosis, that their daughter products unite in the 

 second spermatocytes and there undergo a reductional division. Diplosomes of this 

 behavior Wilson called the " idiochromosomes," and he correctly noted that they are 

 unequal in volume ; in Nezara alone he states that they are equal, but even here I 

 find that there is always a slight voluminal dififei'ence. They always remain more or 

 less dense and compact during the growth period ; and in most cases they conjugate 

 early in the growth period as I had previousl}' described, but, as Wilson first demon- 



