* 
386 Agassiz on the Relations between Animals 
which exist between animals and the media in which they live, 
than the vague views which have prevailed lately from want o 
investigation of the subject rather than from an especial view 
taken of it; Iam far from supposing that in every instance I 
have hit at the outset the true view. I shall be satisfied to have 
called forth direct investigation upon this question, and led the 
way in a field which promises so ample reward. 
Before entering into a special investigation of the natural rela- 
tions of Vertebrata and the surrounding media, it may not be out 
of place to call attention to some collateral facts which will appear 
particularly prominent in the type of Vertebrata, but which have 
already their value in the study of the lower types. I allude to 
the relative bulk of animals of the same type living in different 
di e can derive no impression upon this point from the 
investigation of Radiata, as they are all aquatic, and almost en- 
tirely marine. But the difference is already marked between 
Mollusca if we contrast their marine and their fluviatile and ter- 
restrial types within the limits of their natural secondary groups. 
Among Articulata the same rule obtains, and here we may 
compare classes with classes, even in their different stages of 
wth. Are not the Worms, taken as a whole, larger animals than 
the Caterpillars? Do we not find among, marine Worms by far 
the largest types? We need only remember the gigantic Eunice, 
or even the parasitic Tape Worms'to be satisfied of the fact. Are 
not the Crustacea as a class composed of types exceeding far the 
aan ot Insects even with their wings spread? Are not the 
Lobsters many times larger than the fresh water Craw 
