A bathymetrical division defines the classes of animals according to the depth of water in which they live. Those which live near the shore are /littoral/ species, those of the broad sea are /pelagic/, while those living at great depths are /abyssal/.
Their modes of life are distinguished by other terms. Those which float at or near the surface and are carried about by the currents, like the jellyfishes and the minute organisms mentioned elsewhere, are /plankton/. Strong swimming animals which move about at will are /nekton/. Those which are fixed, like oysters, sponges, etc., and those which crawl on the bottom, like crabs, echinoderms, etc., are /benthos/.
Again, geographical divisions are named, in recognition of climatic influences. The /boreal/ fauna and flora on the Atlantic [pg024] coast extend from Cape Cod northward; the /American/, from Cape Cod to Cape Hatteras; the /West Indian/, from Cape Hatteras southward. On the Pacific coast the divisions, without definite names, are from the Isthmus to Acapulco, Acapulco to the Gulf of California, Cape Lucas to the Strait of Fuca. These divisions merge at indefinite lines, but the above limits are generally accepted as the points of broad division.
The shore or littoral fauna is especially abundant and comprises more species that are curious in form and beautiful in color than the others. The invertebrates of the deep sea are mostly transparent and of a blue or violet tint, while the fishes are gray or bluish above and white beneath, which renders them inconspicuous to their enemies. [pg025]
The vegetable world is separated into two great divisions: /thallophytes/, or plants having no distinction of leaf or stem, and /cormophytes/, or plants which have leaves and stems. All thallophytes that live in the water and are nourished wholly by water are called /algæ/.
A second great division of plants is into /cryptogams/, or those that have no flowers, and /phanerogams/, or those that have flowers, by means of which seeds are produced and successive generations of plant life continued.
/Thallophytes/ and /cryptogams/ comprise the lowest and simplest vegetable organisms. Algæ belong to both these divisions; to the first because they have neither stems nor leaves, and to the second because they have no flowers.