16 NATURAL ARRANGEMENT OF INSECTS. 



Analogies of the ANNULOSA to the TESTACEA. 



Analogical Characters. 



rPre-minently typical; head dis-} 



1 tinct, with long antenna? or ten- > GASI 



C tacula 3 



Classes of the Analogical Characters. 



Annulosa. 



f Mouth surrounded with long ten- 

 ns ; .soft parts of 



DlTHYRA. 



( a shell. 



Oe most simple in their organ-} 

 T% gf&JuSrf S- [ PATA. 

 :hiae. . 3 



rDisk of the belly flattened, and} 



ANiNELiDES. < often performing the office of a V NUDIBRANCHIA. 



t foot. 3 



The high development of the head and of the antennse 

 are not the least remarkable characters of the Ptilota, or 

 typical insects ; while, at the same time, it is all but 

 universal in the Gasteropoda to find the head distinct, 

 and the tentacula, representing antennse, more or less 

 developed. The reverse of this, however, takes place 

 in the apterous insects (Aptera), and the bivalve shell- 

 fish (Dithyra) : the whole of the spiders and scorpions 

 are familiar examples, setting aside the crabs, where the 

 whole body at first sight appears turned into a head, 

 without, however, its limits being at all defined. The 

 Dithyra, or bivalve shellfish, are absolutely headless, 

 and live, like their prototypes, entirely by suction. The 

 analogies between the barnacles (jCirrhipedes) and the 

 cuttlefish (Cephalopoda) are even more striking to an 

 ordinary observer than the former instances. Both have 

 the mouth surrounded by long flexible arms, with which 

 they seize their prey and convey it to their mouth, placed 

 like that of the radiated animals, in the centre; and in both 

 are numerous animals whose body is protected by shells. 

 The strong analogy, as was formerly observed *, between 

 the Parenchymata and the annulose Vermes has induced 



* Malacology, p. 52. 



