GRADATION AMONG ANIMALS. 85 
group as compared with the other; they stand 
on one structural level, though with different 
tendencies, — the body in Mollusks having always 
a soft, massive, concentrated character, with 
great power of contraction and dilatation, while 
the body in Ariticulates is divided by transverse 
articulations, and has nothing of this compact- 
ness and concentration, but, on the contrary, is 
usually marked by a conspicuous external dis- 
play of limbs and other appendages, and by a re- 
markable elongation of the body, — that feature 
characterized by Baer when he called them the 
Longitudinai type. There is in the Articulates 
an extraordinary tendency toward outward ex- 
pression singularly in contrast to the soft, con- 
tractile body of the Mollusks. We need only 
remember the numerous Insects with small bod- 
ies and enormously large wings, or the Spiders 
with little bodies and long legs, or the number 
and length of the claws in the Lobsters and 
. Crabs, as illustrations of this statement for the 
- Articulates, while the soft, compact body of the 
Oyster or of the Snail is equally characteristic of 
the Mollusks ; and though it may seem that this 
assertion cannot apply to the highest class of 
_ Mollusks, the Cephalopoda, including the Cuttle- 
Fishes with their long arms or feelers, yet even 
these conspicuous appendages have considera. 
ble power of contraction and dilatation, and in 
