26 ETHEL NICHOLSON BROWNE. 



EXPLANATION OF PLATE I. 



Notonecta undulata. Figs, i, 2, metaphase of first division showing 14 chromo- 

 somes, two small ones in the center. Figs. 3, 4, initial anaphase of first division, 

 side view, two small pairs in the center. Fig. 5, metaphase of second division 

 showing 13 chromosomes, large idiochromosome in the center. Figs. 6, 7, the 

 same, but both idiochrosomes showing in the center. Fig. 8, initial anaphase 

 of second division, side view, idiochromosome-pair in the center. Fig. 9, the 

 same, but idiochromosomes on different fibers. Fig. 10, A and B, sister anaphase 

 groups of second division, from the same spindle. Fig. n, spermatogonial group 

 showing 26 chromosomes. 



All the figures were drawn with a camera, 1/12 oil immersion and a 12 com- 

 pensation ocular, then reduced in the engraving to two thirds. 



