400 
ON THE STRUCTURE AND HABITS 
Kingdom by a tribe of beings which have generally been considered as the simplest 
form of animals.* 
If, at this season of the year, we have recourse to any pond, brook, or exposed 
piece of water, and take but a single drop of their contents, we shall find by the 
aid of the microscope, though invisible to the naked eye, we have secured a 
little world full of life and motion teeming with inhabitants, endued with 
instincts and functions as calculated to afford happiness as those we see possessed 
by the more complicated tribes of beings that cover the surface of the immense 
globe we live uponfi. 
* In the following observations I have adopted in some measure the arrangement of Mr. Kirby 
in his Bridgewater Treatise , as being the most popular work on the subject; but since this differs 
considerably from the classifications of recent writers, I have drawn up a list of the classes with 
their sub-kingdoms, as far as I intend to illustrate them, and given a familiar example of each, 
according to the views of Dr. Grant, Professor of Zoology and Comparative Anatomy in the 
London University:— 
Sub-kingdom I.—Radiated or Cyclo-neurose Classes. 
Class. Example. 
1. Polygastrica Vinegar Eel, Monas, Volvox. 
2. Poriphera Common Sponge. 
3. Polypiphera Coral, Madrepores. 
4. Acalepha Jelly-fish, Portuguese Man-of-War, 
5. Echinoderma Star-fish, Sea-urchin. 
Sub-kingdom II.— 
6. Entozoa 
7. Rotifer a 
8. Cirrhopoda 
9. Annelidce 
10. Myriapoda 
11. Insecta 
12. Araehnida 
13. Crustacea 
Sub-kingdom III.—Molluscous 
14. Tunicata 
15. Conchifera 
16. Gasteropoda 
17. Pteropoda 
18. Cephalopoda 
or Diplo-neurose Classes. 
Tape-worm, Fluke, Hydatid, 
Wheel-animalcule. 
Barnacle-shell, Sea-acorn. 
Earth-worm, Leech. 
Plundred-leg, Millipede. 
Fly, Beetle, Bug. 
Spider, Scorpion. 
Crab, Shrimp, Lobster. 
or Cyclo-gangliated Classes. 
Pyrosome. 
Cockle, Oyster. 
Snail, Whelk, Periwinkle. 
Hyalea. 
Nautilus, Cuttle-fish. 
These sub-kingdoms are founded on the different arrangements of the nervous system in the 
various classes which they comprehend. In the first the nervous matter is either diffused through¬ 
out the whole animal in a molecular form, or in a circular form, as Fig. 6. In the second the 
nervous matter is arranged in two parallel lines as in Fig. 5. In the third the general arrange¬ 
ment of the nervous system is circular, but its continuity is interrupted by little swellings called 
ganglions, as in Fig. 7. 
f We presume Mr. Lankester here intends merely to state that every animal, however low in 
the scale, is so organised as to possess a certain degree of happiness, and to prevent its being 
