130 
ON THE STRUCTURE AND HABITS 
The Earth-worm has an external structure similar to that of the Leech; it is 
externally composed of segments, w r hich permit the animal to make those con¬ 
tortions we so often observe ; but it has, added to each of these segments, a little 
organ which can be regarded in no other light than the element or commencing 
existence of a leg. On each of the segments the Earthworm has four pair of 
these little legs, two pair on each side; and they are supplied with a delicate 
muscular apparatus, by which the animal is enabled to use them as organs 
of motion. 
Amongst the Annelidans are many that inhabit the sea. One of these, the 
Serpula , or Wormshell, inhabits a shell. Another called Sabella , buries itself 
in the sand, and there throwing out a viscid secretion from its skin, a hard 
covering is formed for it by the glued sand. In some districts these animals are 
the means of throwing-up in this manner sand-banks of considerable size. They 
first bury themselves in the sand, with the exception of their heads, which 
remain out for the purpose of securing their prey. In the course of a little time 
the sea, as the tide rises, will wash the sand and shingle over them; the animal 
then elevates itself in its case, till its head is above the fresh deposited sand. As 
their cases are firm, they give enough strength to the sand to enable it to resist 
the effect of the retiring tide. When the tide again comes up, it deposits more 
sand, which the Sabellce still rise above and consolidate; and in this way consi¬ 
derable elevations of sand are produced. 
As we proceed higher in the scale of animal life, we find every part becoming 
more complicated. In the anatomy of the animals we have been so rapidly 
glancing at, we shall find this fully confirmed. But still we meet with no new 
function performed—no higher ends attained by the more complex than by the 
more simple forms of animal life. We found the little animalcules exercising all 
the functions of organic and animal life; and now that we have gone through 
more than half the classes into which animated beings are divided, we still find 
the same functions performed, but with more complicated apparatus. 
Had it been the object of this paper, it would perhaps not have been unin¬ 
teresting to have pointed out the gradual development of organs that takes 
place in the animal kingdom, in order to show how beautifully gradual are the 
steps by which the Creator has proceeded to form that masterpiece of the animal 
creation, Man. 
From the observations previously made, this gradual development will hardly 
be traced, but still the general form and habits of the creatures mentioned will 
have probably suggested the idea. In the class or classes of animals we are 
now about to enter upon, it will be noticed that the skeleton or the organ of 
support is more highly developed than in any of the preceding classes. In fact 
it cannot but have been seen, in passing up from the animalcules and Jelly-fish, 
