Pair of Heterochromosomes in Forfcula 231 



larger and smaller. Therefore, although I have succeeded in find- 

 ing very few cases of a lagging chromosome like that described by 

 Zweiger and shown in Figs. 37 and 38, I am inclined to connect the 

 irregular numbers in second spermatocytes with this chromosome, 

 which, judging from its size, and from the behavior of the super- 

 numerary heterochromosomes in Diabrotica soror and Diabrotica 

 i2-punctata (Stevens '08), I think must be a precocious division 

 of the smaller heterochromosome, Xo. In Fig. 41, e, two of the 13 

 chromosomes are unusually small, lie side by side, and were paler 

 blue than the other chromosomes, a difference which is often notice- 

 able between the larger {xi) and smaller (^2) heterochromosomes 

 in metaphase oi the first maturation mitosis in preparations 

 stamed with thionm. In this case the number, 13, may be due to 

 precocious division of ^2 in the daughter cell to which it passed in 

 the first mitosis. In such cases as are figured in Figs. 37 and 38, if 

 one daughter element of the lagging chromosome goes to each 

 second spermatocyte the numbers should be 12 and 13 with one 

 smaller chromosome in each cell. In Figs. 41, d, f, and^, one of the 

 13 chromosomes is unusually small {s}. The number 11 is more 

 diflrtcult to account for, unless the two heterochromosomes some- 

 times go to the same daughter cell; of this I have seen no evidence. 

 In two cases I found that one chromosome which was out of the 

 equatorial plane had been removed in another section, leaving 11, 

 and in a few spindles seen from the side one chromosome has been 

 considerably out of the equatorial plane. This may account for 

 all of the I I's. All of the figures of 13's (Figs. 41, e-g) were cases 

 where metakinesis had not begun, and it was perfectly certain 

 that 13 distinct chromosomes were present. The chromosomes 

 usually divide regularly as in Fig. 42 and give daughter plates con- 

 taining 12 chromosomes as in Fig. 43, but occasionally one sees a 

 lagging chromosome (Fig. 44) which in some cases is pulled out 

 somewhat irregularly between the two groups of fused chromo- 

 somes as though dividing (Fig. 45), but is more commonly plainly 

 included in one of the spermatids without being divided (Fig. 46). 

 In fact, I have found no case where this chromosome was clearly 

 divided as is the case with the lagging chromosome of the first 

 division (Fig. 37, Xo). This lagging chromosome of the second 



