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 Articulates 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 
Longitudinal 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 
remeimber the numerous Insects with small bod- 
ies and enormously large wings, or the Spiders 
with little bodies and long légs, 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 
