GRADATION AMONG ANIMALS. 87 
Taking first, then, the lowest branch, how do 
the classes stand within the limits of the type of 
Radiates? I think I have said enough of these 
different classes to show that Polyps as a whole 
are inferior to the Acalephs as a whole, and that 
Acalephs as a whole are inferior to Echinoderms 
asa whole. But if they are linked together as a 
connected series, then the lowest Acaleph should 
stand next in structure above the highest Polyp; 
and the lowest Echinoderm next above the high- 
est Acaleph. So far from this being the case, 
there are, on the contrary, many Acalephs which, 
in their specialization, are unquestionably lower 
in the scale of life than some Polyps, while 
there are some Echinoderms lower in the same 
sense than many Acalephs. 
This remark applies equally to the classes 
within the other types; they stand, as an average, 
relatively to each other, lower and higher, but, 
considered in their diversified specification, there 
are some members of the higher classes that are 
inferior in organization to some members of the 
lower classes. The same is true of the great di- 
visions as compared with each other. Instead of 
the highest Radiates being always lower in organ- 
ization than the lowest Mollusks, there are many 
Star-Fishes and Sea-Urchins higher in organiza- 
tion than some Mollusks; and so when we pass 
from this branch to the Articulates, if we assume 
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