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 

 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 



