1 34 LIED, IN ITS INTERMEDIATE EORMS. 
text of a lecture ; but still, if the function of the palate 
have not utterly extinguished that of the eye, they can 
scarcely have picked one of thoso dainty animals to pieces 
■without having observed that it is encased in a sort of 
armour composed of many rings, the edges of which over- 
lap, and which thus work one within the other. This 
circumstance forms the most prominent characteristic of 
a grand division of living beings, which are thence called 
Annulosa (ringed), or Articdi.ata (jointed). Another 
mark of distinction is that their skeleton is external ; the 
outer skin, hardened in most cases into a horny crust, 
affording attachment to the muscles, and giving by its 
solidity aud resistance precision and force to their con- 
tractions. In some cases, indeed, this structure is less 
obvious, the skin being rather membranous than crusta- 
ceous, but even there it is more tough and leathery than 
the internal parts. 
But the most important distinction of all, though it is 
one which is appreciated only by the anatomist, is the 
condition of the nervous system. That remarkable sub- 
stance, neurine — which is the material seat of all sensation, 
and the proximate source of all motion, the ultimate link 
of matter, whereby the spirit lays hold of it — is either 
not discernible at all in the inferior creatures we have 
been considering, or else exists only in the form of slen- 
der threads, without any centres of accumulation. We 
now no longer find it in this rudimentary condition. In 
the Articulate animals there is a distinct arrangement of 
the nerves, which, in general, run down the middle of the 
body in two parallel cords, united at certain intervals by 
knobs or aggregations of the nervous substance, called 
