293 



Several important facts brought out by the preceding comparison are worth 

 consideration. 



1. No two of the ages here compared are alike in all the characters. 



2. In the anal fin and soft dorsal there is a definite increase in the number 

 of rays with the age. 



3. Variation of this nature is not present in the other structures. 



4. The extent of variation in the different ages is about the same. 

 Dorsal Rays. — The average number of dorsal rays are 14.57, 14.76 and 14.98 



for the first, second and third year specimens, respectively. There is a slight in- 

 crease with age. The summaries for this structure are given below in Table XI, 

 and the curves in Fig. 8. The prevailing number of rays is 15 for all three ages, 

 the per cents, being 53.39, 52 53 and 55.69 for the first, second and third year 

 specimens, respectively. The per cent, of specimens having 14 rays decreases from 

 40.72 in the first year to 22.35 in the third year specimens, while the per cent, of 

 specimens having 16 rays increases from 3.38 in the first year specimens to 16.73 in 

 the third year specimens. The extent of variation is from 12 to 16 in the first 

 year, from 12 to 17 in the second year and from 13 to 18 in the third year speci- 

 mens. As in the anal fin there is a tendency toward a greater number of rays as 

 the fish grows older. 



70 



50 



43 



30 



20 



10 



ti 



m 



12 13 14 .5 16 17 if) 



Fig. 8. 



