m'clung: chromosomes of anasa tristis. 375 



the accessory chromosome in this spireme condition is accom- 

 panied by a large distinct plasmasome which lies toward the 

 center of the nucleus. Such a structure is absent from the 

 photographs presented by Foot and Strobell when the accessory 

 chromosome (their plasmasome) is elongated. As will be noted 

 in Miss Pinney's description, the plasmasome does not appear 

 until after synizesis is established. Some of the nuclei figured 

 by Foot and Strobell would seem to be presynizetic in develop- 

 ment and could not therefore contain plasmasomes. 



I would conclude, therefore, that after synizesis there are 

 present in the first spermatocyte nuclei two nucleolus-like 

 bodies, one the accessory chromosome and the other a plasma- 

 some. Further, that the accessory chromosome exists through- 

 out the whole period, for a time, as a short, heavy thread, at 

 other times concentrated into a mass, and finally in the late 

 prophases as a straight longitudinally split rod. The plasma- 

 some, on the other hand, is an inconstant structure, absent be- 

 fore synizesis, and again in the late prophase, and is not to be 

 mistaken for the accessory chromosome. 



5. What is the behavior of the accessory chromosome in the 

 first spermatocyte mitosis? 



Reference has already been made to the condition of the ac- 

 cessory chromosome in the late prophase and to its position in 

 the equatorial plate. It appears in the metaphase as a uni- 

 valent, longitudinally split rod lying outside the ring of ordi- 

 nary chromosomes. In division its halves separate and during 

 the anaphase move to the two poles of the spindle as do those 

 of the other chromosomes. Examples of this may be seen in 

 figures 2, 3, 4, 5, 6, 7, 8, 9, 10, plate LXXI. Both series of 

 daughter chromosomes may be seen in plate LXXI, figure 3, 

 which shows a mid-anaphase with the halves of the accessory 

 chomosome accompanying each group. There appears to be no 

 question on the part of anyone regarding the movements of the 

 chromosomes in the first spermatocyte, so that an extended dis- 

 cussion on this point is not called for. 



From the fact, however, that Foot and Strobell have used the 

 tardy division of the accessory chromosome in the first sperma- 

 tocyte as an argument to prove its division in the second 

 spermatocyte, because here also it lingers for some time near 

 the equatorial plate after the other chromosomes have moved 

 toward the poles of the spindle, it will be necessary to call at- 



