OF INVERTEBRATE ANIMALS. 
129 
“ These concealed 
By the kind art of fav’ring Heaven, escape 
The grosser eye of Man •, for if the world 
In worlds enclosed, should on his senses burst, 
From cates ambrosial, and the nectar’d bowl 
, He would abhorrent turn, and in dead night 
When silence sleeps o’er all, be stunn’d with noise.” 
Thomson. 
But as the detail of the structure and habits of these animals might alarm some 
readers, I shall merely add, in the words of a writer on this subject, that 44 more 
than twenty of these pestiferous creatures that attack Man have been enumerated; 
some penetrate into the very seat of thought; others disturb his bile; others 
circulate with the blood in his veins; others, again, are seated in his muscles; 
others in his stomach; the Guinea-worm in his cellular tissue; some attack one 
part, some another; some even attack infants, and them only. Such are the 4 ills 
that flesh is heir to.’ ” 
The next group of the lower animals is the one which includes the Common 
Earth-worm and the Leech. The structure of these, which are called Annelidans, 
is very curious and interesting, not failing to offer as many proofs of creative 
wisdom and goodness as those which receive more attention from the general 
observer. The Leech is well known for its important services as a phlebotomist. 
The instruments which it uses in this capacity are three serrated teeth, which it 
very adroitly projects into the flesh, and afterwards applies to the wound a sucker, 
by means of which it is enabled to withdraw, from the part it wounds, a large 
quantity of blood. They are found numerously in our pools and ditches, and 
subsist there by preying upon the animalcules and other animals that live in 
those places. There are two kinds found in this country, the Horse Leech and 
the Medicinal Leech. To be able to distinguish between these is a point some¬ 
times of great utility, as the former is by no means so adroit and clever a surgeon 
as the latter, and frequently his awkward surgery is attended by unpleasant 
effeqts. The Horse Leech is much longer, and has a greener, brighter, and more 
varied colour than the Medicinal Leech. It also inhabits stagnant waters, 
whilst the other is found in brooks and running streams. Although the Leech 
occurs very plentifully in many parts of this island, yet such is the quantity 
used in this country, that many thousands are actually imported from the 
continent. 
If we examine the structure of the Leech, we shall find that externally it is 
composed of a series of rings, which are in fact, its skeleton, giving attachment to 
its muscles, and support and defence to its organs. It is here, then, the rudiments 
of that skeleton commence, which we find completed in the higher forms of 
animals, as the Crabs and insects. 
