CHROMOSOME STUDIES 245 



of the chromosomes of a large number of individuals belonging 

 to species of both these genera, I became acquainted with the 

 form, the relative length, and the behavior of what appeared 

 to be the normal chromosomes. I was able with little diffi- 

 culty to distinguish the members of a pair from each other, by 

 means of their length. When an individual was found showing 

 one chromosome in a pair of slightly abnormal length, I was 

 able to determine to which pair of chromosomes it belonged, 

 whether to the 4's, or I's, etc. This enabled me to trace its 

 course in the maturation division. As a result I found that 

 it separated from its mate in the first spermatocyte division, 

 and divided equationally in the second. On passing to the pole 

 of the first division these abnormal members showed that they 

 were split longitudinally in preparation for the next division 

 (no. 1 in fig. 147), which was equational. The length of the 

 abnormal chromosome in the late metaphase, as the result of 

 the constriction of the tetrad, or in the anaphase after separa- 

 tion from its mate, agreed in each case, when compared with 

 the rest of its fellows, with the length of the chromosome in the 

 diploid divisions. This may be seen by comparing the deficient 

 4's (4-) in figures 115 and 104 or 105, and likewise by comparing 

 the abnormally long no. 1 's in figures 141 to 147 with those in 

 figures 136 to 140. 



The above are not the only instances of unequal homologous 

 chromosomes separating from each other at this division. Hart- 

 mann (March, 1913) was the first to recognize — in the primary 

 spermatocytes of Schistocerca — what he termed 'unequal divi- 

 sions' of tetrads. Carrothers later (December, 1913) likewise de- 

 scribed a large number of cases of the unequal division of one tet- 

 rad among the three smaller pairs of chromosomes in the twenty- 

 three-chromosome grasshoppers Arphia simplex, Dissosteira 

 Carolina, and Brachystola magna. There are probably addi- 

 tional divisions of this kind among the larger tetrads of these 

 grasshoppers, but it will be more difficult to recognize them 

 on account of their greater lengths, a slight variation showing 

 less easily in a long chromosome pair than in a short one. 



