294 



TABLE XL 



Dorsal, Spines. — The averages for this structure are 14.69 for the first year, 

 14.39 for the second and 14.65 for the third year, the first and third years being 

 almost identical, and the second year having a fewer number. Fig. 9 represents 

 the curves for this structure. The curves of the first and third years are almost 

 identical, both showing a preference for 15, with about 35 per cent, for 14. The 

 second year shows as decided a preference for 14, about 35 per cent, for 15. This 

 structure varies from 13 to 16 in the first year specimens, from 12 to 17 in the 

 second year specimens and from 13 to 17 in the third year specimens. Table X 

 contains the summaries for this structure. 



60- 



