Zoological Society. 141 



body originally similar may be changed — the progression of indivi- 

 duals does the same thing. The larval condition of insects undoubt- 

 edly corresponds very nearly with the Annehda ; the arrangement of 

 the body and the relation of each segment to the nervons system "are 

 similar. But the perfect state shovFS a very great modification in the 

 form ; many segments have disappeared by coalescence, vs^hilst the 

 equality of size originally existing betvreen them has been lost by 

 reason of the centralization of functions ; the nervous centres have 

 often been removed from their respective segments, yet the number 

 remains the same ; for although only nine centres appear in the abdo- 

 men (Blanchard sur les Coleopteres, Annales des Sciences Naturelles, 

 1846, part i.), yet the last has been shown in the Lepidoptera (New- 

 port on Sphinx, Phil. Trans. 1832) to consist of two which have 

 united. 



4. The same segmental arrangement of the body, and the same 

 ganglionic condition of the nervous centres in accordance with the 

 rings of the body, obtain throughout many members of the class of 

 the Articulata. 



We now descend to two more particular propositions, resulting 

 from and embraced in the foregoing, but which we nevertheless pre- 

 fer to illustrate separately. 



There are reasons to expect that the head of the Vertebrata should 

 be composed of segments similar to those of the body. 



1. "We have already noticed the close resemblance between the 

 anterior segment or head and the following ones in the Polydesmidce. 



2. In the larval insects the similarity is great ; but in the perfect 

 one a number of the other segments become anchylosed, and enter 

 into the composition of the head, in accordance withthe law, that the 

 more perfect an animal is, the more complex and individualized are 

 its parts, and consequently the more is its abstract nature hidden 

 under its teleological manifestation. The divisions between the seg- 

 ments entering into the composition of the head sometimes remain 

 permanently recognizable in the external skeleton. The number of 

 these segments has been a much-vexed question among entomolo- 

 gists, the numbers advocated by different naturalists having been two, 

 three, four, five and seven. I am inclined to believe the real number 

 of these segments to be four : — 1st, because of the very slight evidence 

 for the presence of any other, the fifth segment being considered as 

 entirely atrophied, and no corresponding manducatory organ ap- 

 pearing ; 2nd, from four being the only number at all discoverable in 

 some insects, as in the Hydrous piceus (see Newport on Insecta in 

 Todd's Cyclopaedia) ; 3rd, because the brain (i. e. the coalesced 

 ganglia of the cranial segments) of the Necrophlagceophus longicornis 

 has been discovered by Newport, at the period of its bursting its 

 shell, to consist of four double ganglia (Newport in Phil. Trans. 

 1843). 



We next consider the reasons for supposing that the organs com- 

 posing the mouth of the Vertebrata should be the homologues of 

 those of locomotion. It must be remarked, that everything now to 

 be said assists most strictly in support of the preceding proposition, 



