NEW TYPES OF CHROMOSOME DISTRIBUTION. 123 



will be used in reference to the chromosomes of the triad, tetrad, 

 pentad and hexad groups. 



DESCRIPTIVE. 



Diplocodus e.i'sanguis Stal. 



In Diplocodus we find a typical pair of idiochromosomes as 

 described by Wilson ('05) for several species of Hemiptera. A 

 description is included here mainly to show the range of vari- 

 ability in chromosome distribution found within the limits of a 

 single family of Hemiptera. There are 26 chromosomes in the 

 somatic groups of both male and female cells (Fig. I, A, B, C 

 and D}. AYhile there is very little difference in size in the 

 idiochromosomes, there is one chromosome in the male group, 

 noticeably smaller than the others, which without doubt, is the 

 small idiochromosome. As the idiochromosomes are separate 

 in the first division, the metaphase plate of the first division 

 shows 14 chromosomes (Fig. i, E and F), one more than half 

 the spermatogonial number. In these figures, the small idio- 

 chromosome can be readily identified, but one cannot always 

 be sure of the large one. Both divide in this division. In the 

 second division, there is a rearrangement of the chromosomes, 

 12 taking up the position of a ring with the idiochromosomes, 

 one above the other, in the center (Fig. i, / and /, side views of 

 the second division, metaphase). A polar view of the metaphase 

 accordingly shows only 13 chromosomes. Wilson figures them 

 as coming into close apposition at this time to form an asym- 

 metrical dyad. While I have not examined a large number of 

 cases in Diplocodus, they, here, seem not to fuse, but only to come 

 very close together as shown in Fig. i, /. Fig. i, /, shows that 

 their separation precedes the division of the chromosomes in the 

 ring, as is also the case in the forms described by Wilson. Fig. 

 i, K and L, represent two anaphases taken from the same spindle. 



The history of the idiochromosomes during the growth period 

 has not been fully traced. In the contraction-phase (Fig. i, M}, 



mosome stains intensely black, while in O it is pale and the idiochromosomes 

 can be seen lying embedded in it ; P is a prophase figure of the first division, 

 showing the idiochromosomes in marked contrast to the looser masses of 

 chromatin condensing to form the remaining chromosomes. The enlargement 

 is 3,726 diameters. 



