16 



NATURAL ARRANGEMENT OF INSECTS. 



Analogies of the Annulosa to the Testacea. 



Classes of the 

 Annulosa. 



Ptilota. 



Aptera. 



CiRRHIPEDES. 



Vermes. 



Annelides. 



Analogical Characters. 



rPre-minently typical; head dis-^ 

 j tinct, with long antennx or ten- > 

 L tacula, J 



'Sub-typical; head indistinct, often 'J 

 I confounded with the thorax, or f 

 i altogether wanting; antenna f 

 . or tentacula often wsmting. J 

 'Mouth surrounded with long ten-^ 

 ) tacula or arms; soft parts off 

 I the body generally protected by f 

 ' a shell. 3 



"The most simple in their organ- ^ 

 \ isation ; naked; without limbs f 

 ^ of any sort; destitute of bran- f 

 . chis. 3 



-Disk of the belly flattened, and 

 often performing the office of a 

 . foot. 



Tribes of the 

 Testacea. 



Gasteropoda. 



DiTHYHA. 



Cephalopoda. 



Parenchymata. 



NUDIBRANCHIA. 



The high development of the head and of the antennae 

 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 antennae, 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 (^Cirrhipedes) and the 

 cuttlefish (^Cephalopoda) are even more striking to an 

 ordinary ohserver 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. 



