. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIG. i. CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 25 ously described as the last generation of primary spermatogonia), lie in the follicle without definite arrangement and are usually much flattened and distorted by mutual pressure and that of the growing spermatocysts between which they lie. For this reason a study of the chromosome series is difficult in this cell-genera- tion, but, fortunately, I have been able to find a few division-figures which per- mit of an accurate study of the chro- mosomes. Such a cell as that shown
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIG. i. CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 25 ously described as the last generation of primary spermatogonia), lie in the follicle without definite arrangement and are usually much flattened and distorted by mutual pressure and that of the growing spermatocysts between which they lie. For this reason a study of the chromosome series is difficult in this cell-genera- tion, but, fortunately, I have been able to find a few division-figures which per- mit of an accurate study of the chro- mosomes. Such a cell as that shown in Fig. i—a metaphase in polar view- offers the best opportunities. Here it is apparent at a glance that the chromo- somes are of a variety of sizes, but yet in general so nicely graded as to form an almost regular series from smallest to largest. A second glance, however, reveals the fact that there is one very prominent break in this graded series, separating the six smaller chromosomes from the remaining larger ones, and a count of the larger group shows it to contain seventeen units, giving as a total the odd number The odd or twenty-third member of the group, as can be plainly seen in the following division, is the accessory chromosome, which on account of its peculiar be- havior will be considered separately. There is, therefore, in the ordinary group, the even number, twenty-two. More especially in the smaller group, but like- wise in the members of the sixteen, it can be seen that the gradations in volume are not between individual chomosomes but between pairs, the two members of which in each case are of approximately equal 1 Montgomery (/. c.) has found four of the Hemiptera-heteroptera to possess an odd somatic number of chromosomes and I have observed the same to be true for some fifty species of Acrididse and FIG. i. Polar view of metaphase of first genera- tion of secondary spermato- sonia. Six small chromo- o somes designated by lett
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
