132 bulletin: museum of comparative zoology. 



is not constituted of homologous simple chromosomes. Aside from 

 this there seems to be nothing to contradict the view that the tetrads 

 represent the union of homologous paternal and maternal elements.'' 

 Such unsymmetrical loops always occur in Stenobothrus in the case 

 of two of the larger bivalent chromosomes, as has been previously 

 described in detail (Cf. Plate 6, Fig. 93). Sutton (:02) states that in 

 Brachystola the first division is equational, but does not describe the 

 process in detail. In Syrbula there is a prereduction, according to 

 Montgomery (:05), and my results are a complete confirmation of his. 



Voinov (:03) has described a post- reduction in Cybister, a coleop- 

 teron, but Holmgren (:02), Nowlin (:06), and Stevens (:06") have 

 found a prereduction in various forms of the same group. In the 

 myriapods Blackman (:05, :05'\ :07) has described a postreduction, 

 but the chromosomes in these forms appear to be very unfavorable 

 for determining the sequence of the divisions, and I think are suscepti- 

 ble of either interpretation. This author lays much stress on the 

 fact that in the early prophase the longitudinal cleavage appears 

 before the transverse becomes evident and that it is but natural, 

 therefore, to believe that the longitudinal division is the first to be 

 completed in the two following mitoses. If the two divisions were of 

 the same kind, no doubt this would be reasonable, but since they differ 

 so fundamentally it is a question if the argument is valid. 



Stevens (:03, :04) has found a ])rereduction in the spermatocytes 

 of Sagitta and a postreduction in the oocytes of the same form, but 

 her figures are inconclusive. 



It remains to consider the cases in which two transverse divisions 

 have been described for the Orthoj:)tera. Wilcox ('95) maintained 

 that both divisions are transverse in Caloptenus (Melanoplus), but as 

 his results have been generally discredited it is unnecessary to consider 

 them here. Apparently Wilcox's fundamental error was in assuming 

 that there are twelve chromosomes in the spermatogonia, whereas 

 there are in reality twenty-three, as in the majority of the Acrididae. 

 Recently Otte (:06) has described two transverse divisions in Locusta, 

 but his results differ fundamentally from those of Wilcox, since he 

 believes that neither is a reducing division in Weismann's sense. 

 According to this author the chromosomes conjugate side by side 

 during synapsis. Later the double threads thus formed shorten and 

 thicken, while the free ends often ajiproach each other and may fuse 

 to form rings. "Da nun die Ringe durch Umbiegung eines Doppel- 

 fadens entstanden waren, so ist die, 1. Rcifungsteilung cine Quertei- 

 lung des urspriinglichen Doppelfadens. Der Doppelfaden war durch 



