lo University of Michigan 



at the end of this period. From this time on there is a sud- 

 den decrease in the growth rate up to the third year, when the 

 rate becomes constant until between the fifth and sixth years, 

 when there seems to be a slight increase again. This may 

 accompany changes that eventually lead to metamorphosis. 

 No data are available for a comparison of the size of the full- 

 grown larva with that of the adult. Since the animal does 

 not feed after metamorphosis, it is likely that there is no 

 increase subsequent to this period. Neither is it likely that 

 there is any decrease in size during or after metamorphosis, 

 as Meek (1916) has suggested. 



Reduced to percentages, the growth increments for the suc- 

 cessive years of larval life are found to be as follows : 



Age Thunder Bay River Gilchrist Creek 



o to 3 months 19.0% 18.1% 



3 months to ij4 years 26.1% 27.2% 



iJ4 years " 2% " 11.9% 13.6% 



2}i " "3^ " 9.5% 9.0% 



3'A " "414 " 9-5% 9-0% 



4% " " S'A " 9-5% 9-0% 



sVa " "654 " 14.2% 13.6% 



From the above table and from the graphs it will be seen 

 that the rate of growth differs somewhat in the two collections. 

 The rate is a little higher in the brook collection during the 

 first and second years. This variation may, of course, be 

 within the limits of error due to the small size of the series, 

 but if any meaning can be attached to it, one might suggest 

 the cause to lie in differences in food conditions, differences 

 in temperature, or some other factor which might favor the 

 brook-living individuals. 



Mortality Rate. — By grouping the larvae that approximately 

 belong to each year in the life cycle of the animal, it is pos- 

 sible to obtain some idea of the annual death rate. One can- 



