92 ETHEL NICHOLSON BKOWNE 



by Paulmier and other early observers of the insects. In some 

 respects Notonecta is not well adapted for the elucidation of this 

 problem, owing to the difficulties attending the study of the chro- 

 mosomes during most of the growth period. On the other hand, 

 this form offers certain advantages in the fact that the formation 

 of the rings and crosses may be clearly followed during the pro- 

 phases. The facts here seen seem to leave no doubt that the 

 rings are formed in essentially the same way as in the Amphibia 

 and Tomopteris, though their relation to the original spireme can 

 not be traced. 



Those observers (Gregoire, the Schreiners, and many others) 

 who accept a side-by-side conjugation, or parasynapsis, regard the 

 ring as originating by the opening out of the longitudinally split 

 spireme. Those observers (Paulmier, McClung, et al.) who accept 

 an end-to-end conjugation, or telosynapsis, regard the ring as 

 originating by the bending together of the split spireme at the two 

 extremities. In either case, the final result is the same as far as 

 the real significance of the ring is concerned. The plane between 

 the two half rings passes through the synaptic point and there- 

 fore, according to most observers, a division in this plane means a 

 reduction division, the division in the plane of the ring dividing 

 it into two whole rings is longitudinal and equational. According 

 to some observers, e.g., Paulmier, Montgomery, Farmer and 

 Moore, and also most of the adherents of parasynapsis, the first 

 division is reductional. McClung and his students, however, be- 

 lieve that in most Orthoptera it is the second division that is re- 

 ductional. Bonnevie holds that the ring divides in its own plane 

 in both divisions and that therefore there is no reduction; the 

 rings of Enteroxenus, however, have been differently interpreted 

 by the Schreiners ('07). 



In Notonecta it is impossible to trace the chromosomes through 

 the greater part of the growth period when they are aggregated 

 in a karyosphere, but the evidence seems in favor of the hetero- 

 homeotypic scheme of Gregoire. The ring is formed from two 

 parallel rods which probably represent univalent chromosomes. 

 The first division separates the ring into two half rings, and is 

 therefore probably a reduction division. The second division is in 



