OF INVERTEBRATE ANIMALS. 
401 
Amongst the class of animalcules which are called Infusoria, on account of 
their being found so abundantly in vegetable infusions of all kinds, we have 
many of different shapes and sizes, habits and instincts. I have here a repre¬ 
sentation of one of the smallest that is seen by ordinary microscopes, called 
Monas termo , and which is not more than the - 10 ^ of an inch in diameter- 
They are found to possess in their interior several little bags for the purpose of 
receiving their food ; they are in fact stomachs, and on this account they have 
received the name of Polyyastrica. Monas termo is figured in the plate, Fig. 2. 
The propensities of these little creatures do not at all belie their structure ; 
they are most destructive and voracious beings. Every drop of water they 
inhabit is a constant scene of confusion and carnage, on account of their fero¬ 
ciously preying on each other. This, however, is not their only food, for they 
partake abundantly of the vegetable particles that float about in the water with 
which they are surrounded. A singular point in the economy of these little 
animals is their power of retaining their vitality; although they die in their 
natural element in the course of a few weeks, yet if allowed to become dry, they 
will assume their activity on the addition of water for years after. They are 
found in all kinds of fluids, imparting life and activity to the pink dew-drop, 
sparkling in the morning sun, and giving to every drop of the water of the ocean 
millions of inhabitants.* They are found in almost every fluid taken up by 
plants and animals as nutriment; and in the fluid portions of plants and animals 
themselves they exist in abundance. 
I have before observed that no-where in Nature do we find an exact ascending- 
scale of organisation, and accordingly, in the classification of the Animal King¬ 
dom, we are frequently obliged, for convenience, to group its objects according to 
their general properties. Now, then, if by taking the single property of being 
invisible to the naked eye, I group together all animals possessing that property, 
I should expect to bring together animals very dissimilarly formed, for the 
Creator, in the exhibition of his power, does not display to us the most design in 
the largest forms of created beings, but generally treasures up the most brilliant 
miserable: for the proportion of positive happiness must, we conceive, he in direct ratio to the 
degree of development possessed by each animal. It follows, throughout the kingdom, that the 
more organs appertain to the species, and the more complete these organs are, the more will the 
creature enjoy itself, as long as it has the power of employing its organs in the manner intended 
by Nature. The same law which holds good as regai-ds physical matters, is strikingly illustrated 
in mental nature. Thus Man excels all the lower animals in the number and quality of his 
cerebral faculties, and has, therefore, a greater capability for happiness than the brutes. Those 
men, moreover, who act rationally by the greatest number of faculties, and chiefly by the higher 
faculties, are, cceteris paribus , the happiest_ -Ed. 
* Ehrenberg calculates that a single drop of water may contain 500,000,000 of some of these 
Infusoria. 
