340 THE AMERICAN NATURALIST [Vol. LY 



sized nuclei is less than that of specimens with 4 full- 

 sized nuclei, i.e., 176.1 sq. mm. 



4. A further increase in the average size of the speci- 

 mens occurs between the stage with 5 nuclei of equal size 

 (Fig. 5) and that with 6 nuclei, two of which have just 

 emerged from mitosis. Measurements give for the for- 

 mer an average area of 860.5 sq. mm. and for the latter 

 951.4 sq. mm. The specimens with the two small nuclei, 

 however, possess as before (see (2)) a lower average 

 area per nucleus, i.e., 158.6 sq. mm. as compared with 

 172.1 sq. mm. in specimens with 5 full-grown nuclei. 



5. The measurements of the next stage, i.e., specimens 

 with 6 nuclei of equal size (Fig. 7), are more difficult to 

 explain, since the average area of the specimens (926.7 

 sq. mm.) is actuallv less than that of the younger speci- 

 mens (see (4)) with 4 large and 2 small nuclei, and the 

 average area per nucleus falls from 158.6 sq. mm. to 154.5 

 sq. mm. These results may be due to a thickening of the 

 entire animal which would increase the mass and tend 

 toward a decrease in area or the nucleo-cytoplasmic rela- 

 tion may change as the animals become older. That there 

 is an actual decrease in the average area per nucleus as 

 growth proceeds is indicated by the measurements of 

 later stages as given in Table III. This table shows a 

 decrease per nuclear area from 186 sq. mm. in specimens 

 with 4 nuclei to 96.8 sq. mm. in specimens with 29 nuclei. 

 That this decrease is gradual is indicated when averages 

 are made of three successive groups containing each a 

 larger number of specimens. Thus the 4, 5, and 6 nu- 

 cleated groups containing 134 specimens have an average 

 area per nucleus of 173.8 sq. mm., the 7, 8, and 9 nucleated 

 groups containing 136 specimens have an average area 

 per nucleus of 144.4 sq. mm., the 10, 11, and 12 nucleated 

 groups containing 51 specimens have an average area per 

 nucleus of 143.5 sq. mm., and the 13, 14, and 15 nucleated 

 groups containing 13 specimens have an average area 

 per nucleus of 128.3 sq. mm. 



