490 Alice M. Boring 



Many spermatogonia! plates were found, some of which it was 

 possible to count. It seems that there must be one short period in 

 the arrangement of the chromosomes into the plate, when they are 

 spread further apart than at any other time, judging from the 

 behavior of the chromosomes of the first spermatocyte in coming 

 into the equatorial plate, this more open stage must occur when 

 the chromosomes are first drawn into a flat plate from their scat- 

 tered position in prophase. Later as metakinesis begins and the 

 mantle fibers pull from the two poles, the chromosomes are drawn 

 closer together and the diameter of the plate becomes smaller. 

 Fig. 112 shows a very clear spermatogonia! plate, with 19 chromo- 

 somes. It is possible here to group the chromosomes into 9 pairs 

 with one left over; only the two most distinct pairs are lettered, 

 (7, and ^o, long and slender, b^ and b^, a little shorter and thicker. 

 The two chromosomes formed by the fusion of these pairs are 

 designated by a and b in Fig. 114, the equatorial plate of the first 

 spermatocyte, and in Figs. 117 and 118, the equatorial plates of 

 the second spermatocytes. The number of chromosomes in the 

 equatorial plates are what would be expected after finding 19 in 

 the spermatogonia; 10 in the first spermatocytes, and 10 and 9, 

 respectively, in the second. In the rest stages (Fig. 113), a ap- 

 pears as usual, but there are also present two other smaller bodies 

 with the same staining reaction, m^ and )u_. I have called them 

 m-chromosomes, as they have all the characteristics of Wilson's 

 m-chromosomes in the rest stage of the Hemiptera Heteroptera 

 ('05c); they are of equal size and they take the basic stains like the 

 odd chromosome. As unfortunately they are not enough smaller 

 than some of the other chromosomes to be readily distinguished 

 in the spermatogonial plate, or to be traced through the prophase 

 of the first spermatocyte to the spindle, it is impossible to see 

 whether they really represent one pair whose fusion has been delayed. 

 The odd chromosome appears as usual in metaphase (Fig. 115) 

 and anaphase (Fig. 116) of the first spermatocyte division, and as 

 usual is not distinguishable in the metaphase (Fig. 119) or ana- 

 phase (Fig. 120) of the second division. In the spermatids, a 

 basic-staining body appears in half the nuclei (Figs. 121 and I22j, 

 and so must here (as in Entilia and Vanduzea) represent the odd 



