289 



10. The range of variation in the total number of dorsal spines and rays 

 combined is one greater than the variation in the fins separately. 



11. The number occurring most frei^uently is 29 in Turkey Lake and 30 in 

 Tippecanoe Lake. 



12. The preference shown for a gi^en number is less decided for the two 

 dorsal fins taken together than for the dorsal fins taken separately. 



13. The variation is in all cases continuous. 



THE VARIATION IN TTRKEY LAKE. 



Many of the facts on the extent and character of the variation of the (500 

 specimens from Turkey Lake, taken as a whole, have been given in the pre- 

 ceeding. 



The lengths of the 600 specimens from Turkey Lake were measured and upon 

 comparison were found to fall into three quite distinct groups. Fig. f) represents 

 the curve for all. Each of the smaller horizontal distances represents one mm, 

 and each of the larger verticle distances one per cent. The sizes ranged from 27 

 mm. to 102 mm. The first group ranges from 27 mm. to 00 mm.; the second from 

 60 mm. to 80 mm., and the third from 79 mm. to 103 mm. The three curves of 

 Fig. 5 represent these three groups. I have watched the growth during the fir.st 

 summer, and know the first curve to represent the first summer's fish. The second 

 curve in all probability represents the second year's fish, and the third curve, those 

 three years old and over. The growth, thus, is most rapid during the first sum- 

 mer, the rate of growth decreasing each year after. The fish reaches practically 

 its full size the third year, though the more gradual slope to the right of the last 

 curve shows that it does not cease growing entirelv. 



30 35 40 45 50 55 60 65 70 75 80 85 90 SS lOO 



Fig. 5. 



(19) 



