100 bulletin: museum of comparative zoology. 



the spermatogonial chromosomes had failed to pair. He describes 

 two methods of ring-formation. The correctness of his conclusions 

 as to the succession of stages in some of his series might be questioned 

 on the ground that they are not different stages of the same chromo- 

 some. The series shown in his figures 2 to 11 probably represents a 

 normal method of ring-formation, viz., by the opening out of a para- 

 synaptic spireme segment along one of the longitudinal splits, with 

 the ends remaining in contact. The series in figures 12 to 16 might 

 also easily be derived from a parasynaptic segment. It is extremely 

 questionable whether the figures in the series 18-20 are arranged by 

 the author in their natural sequence; the reverse order is more likely 

 to be the correct one. His figures 19 to 27 (Plate 2) doubtless repre- 

 sent different shapes of the same chromosome-pair, the so-called 

 "middle granule" serving to identify the element. I would suggest, 

 however, that the stage that he represents in figure 19 may have 

 resulted from an opening out of a parasynaptic segment in the same 

 way that I have described for chromosome-pair A, in which case the 

 "middle granules" would be polar granules instead of "middle" ones. 

 In view of the rather far-reaching conclusions that Robertson ('15) 

 has drawn from his work on the Tettigidae, I would call attention to 

 some differences, as well as similarities, between his work and mine. 

 In the first place, he describes parasynapsis in the early stages of the 

 growth-period, as I have done, but in the postspireme stages he as- 

 sumes that the conjugants separate along the plane of conjugation 

 (primary longitudinal split), the separation beginning at the proximal 

 end. He shows in the metaphase of the first spermatocyte most of 

 the chromosomes as elongated rods with appearance and orientation 

 similar to that seen for my tetrad A. It will be remembered that in 

 the latter case the separation from the proximal end of the spireme 

 segment toward the distal end is not along the plane of the primary 

 split, but along the plane of the secondary split. I believe that 

 Robertson may have overlooked a similar behavior in the chromo- 

 somes of his material. Curiously enough the unequal elements that 

 he describes are very similar to the unequal type of chromosome B 

 and of chromosome C, in PhrynotettLx. I have shown that the 

 behavior of the cliromatids in B and C is similar to that in A. And 

 that in the cases in which C divides reductionally in the first division 

 the spindle-fiber attachment is necessarily shifted to the distal ends. 

 I believe that such a condition probably occurs in the unequal tetrads 

 described by Robertson, and if so, theoretical explanations, as to 

 how the elements came to be related to each other in the way they are. 



