17 
gone on further; so that all the apparent segments are thus com- 
posed by the anchylosis of two original ones at an early period of 
growth, as proved by the two pair of legs which each one bears, and 
the double nervous ganglia which they contain, the nervous centres 
of the original elements having approximated to one another without 
coalescence (Newport on Myriapoda, Phil. Trans. 1843). 
3. But not only does the progression from lower to higher forms 
in the scale of the animal kingdom teach us how segments of the 
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 Annelida ; the arrangement of 
the body and the relation of each segment to the nervons system are 
similar. But the perfect state shows a very great modification in the 
form; many segments have disappeared by coalescence, whilst the 
equality of size originally existing between 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 Coleoptéres, Annales des Sciences Naturelles, 
1846, part i.), yet the last has been shotwn 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 Polydesmide. 
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 with the 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 Hydroiis piceus (see Newport on Insecta in 
Todd’s Cyclopedia); 3rd, because the brain (7. e. the coalesced 
No. CCII.—Proceepin6s or THE ZOOLOGICAL Society. 
