562 FERNANDUS PAYNE 



in this study, but as no other material is available, my study 

 is limited to sections. I realize that a study of serial sections 

 of side views of a metaphase plate is beset with danger, as the 

 knife may cut chromosomes so as to make them appear as two. 

 However, this has not been such a serious difficulty as it might 

 seem and in the following description I feel reasonably sure I 

 have not made a mistake in this way. Further, these obser- 

 vations have been confirmed by a study of cells in which all the 

 chromosomes are present in a single section. The greatest 

 danger would be in cutting a double chromosome into its two 

 components so as to make it appear as two single chromosomes. 

 In my study of single chromosomes I have been very careful, 

 when two or more are present in a single cell, to see that they do 

 not lie opposite, that is, if the cell were reconstructed the two 

 single ones would not fit together to make a bivalent. 



Side views of metaphase plates with 12 chromosomes show 

 all of them to be bivalent and dumb-bell-shaped (fig. 2, L, M, N 

 and 0). Stevens ('10) described in Forficula auricularia a pair 

 of slightly unequal idio chromosomes. I find here also one of 

 these 12 bivalents (fig. 2, D, i) is slightly unequal. Sometimes 

 no size difference is visible in any of the bivalents and in no case 

 do I find the difference as great as that described by Stevens. 

 Since I have not been able to compare male and female groups, 

 I cannot state definitely whether this unequal pair is related to 

 sex. Even if I had the material for comparison, it is doubtful 

 whether it would yield results, as the size difference is so small. 



I hesitate all the more in saying definitely that it is related to sex 

 since the recent paper of Carothers ('13) describing among the 

 autosomes an unequal pair. 



Side views of metaphase plates with 13 chromosomes show 



II bivalent and two single ones (fig. 2, D, E, F, G, serial sections 

 of one cell and H, I, J, K, of another). This indicates clearly, 

 it seems to me, that two spermatogonial chromosomes have 

 failed to conjugate -at synapsis or have conjugated and then 

 separated. A polar view of such a group looks very different 

 from one with 12, yet the two are the same, the difference being 

 that the components of one bivalent have remained separate in 



