316 CLARK: CORRELATION OF PHYLOGENETIC SPECIALIZATION 



note a maximum development of primitive characters between 

 850 and 1400 fathoms, beyond which point there is a sharp rise 

 so that from 1500 to 3000 fathoms the speciahzed characters 

 are in excess. 



In regard to the . characters under the heading ''General" we 

 should remember that, while the number of component ossicles 

 in the skeleton is of considerable phylogenetic significance in 

 shallow water, it decreases rapidly in importance with depth, 



for the conditions in the 

 abysses are typically such 

 that, chiefly on account of 

 the very hmited food sup- 

 ply, no crinoid can grow to 

 the phylogenetically nor- 

 mal size, and hence all the 

 species are necessarily 

 dwarfs, unable to* develop 

 to the full the skeleton 

 normal to their type. In 

 other words, in the deeps 

 we find a semi-pathological 

 condition inducing degen- 

 eration along the same lines 

 taken by normal phylogen- 

 etic advance. It is this 

 semi-pathological degener- 

 ation simulating phylogene- 

 tic advance which causes 

 the rise in the line repre- 

 senting the figures without 

 those under the heading ''General" from 550-600 to 2500-3000 

 fathoms. This occurs in all the differential characters, but its 

 importance in the skeleton as a whole is here exaggerated for 

 the reason that in "this feature we have included only one con- 

 trasted pair. 



Probably in the present study we are most nearly correct if 

 we take above 250 fathoms the line representing the characters 



Fig. 2. The excess among the recent 

 crinoids of primitive (1) or specialized (2) 

 characters at different depths, including 

 ( ) and without ( ) those un- 

 der the heading "General." 



