362 SYSTEM OF INSECTS. 
i. Lamarck divided the animal kingdom into two pro- 
vinces, or subkingdoms as they are now called ; the one con- 
sisting of all those animals whose skeleton is internal and 
built upon a vertebral column, which are denominated 
Vertebrates; and the second, of those whose skeleton or 
its representative is for the most part external, including 
the muscles, —these are called Invertebrates*. ‘Though 
this distinction is so marked as in general to form a most 
striking characteristic, yet when these two provinces ap- 
proach each other, it begins to disappear. Thus the ver- 
tebral column, forming one piece with the shell”, becomes 
external in the Chelonian reptiles, or tortoises and tur- 
tles, and almost disappears in the cyclostomous fishes ; 
and there is the beginning of an internal one in the Ce- 
phalopoda, or cuttle-fish belonging to the Invertebrates. 
Dr. Virey, assuming the nervous system as his basis, 
long since divided the animal kingdom, without assign- 
ing names to them, into three subkingdoms‘ ; M. Cuvier 
has four—Vertebrata ; Mollusca ; Articulata ; Radiata 
and Mr. MacLeay, finding five variations of that system, 
divides animals into five provinces or subkingdoms, of 
which I formerly gave you some account * ;—viz. Verte- 
brata, in which the nervous system has only one princi- 
pal centre; Annulosa, in which it is ganglionic, with the 
ganglions arranged in a series, with a double spinal 
chord ; Mollusca, in which it is ganglionic, with the gan- 
glions dispersed irregularly but connected by nervous 
threads; Radiata, in which it is filamentous, with the 
‘ nervous threads radiating from the mouth; and Acrita, 
® Vor. TI: p. 10. » Cuv. Anat. Comp. 1, 173. 
© N. Dict. d Hist. Nat, ii. 25, Ibid, 26—. 
° Von. WY. p. 138—. 
