294 



TARI.F XI. 



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 i)reference 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 Hi in the lirst year specimens, from 12 to 17 in the 

 second year specimens and from b'i to 17 in the third year specimens. Table X 

 contains ihv summaries for this structure. 



