802 The American Naturalist. [October, 
uable information upon the phenomena of marine life by a 
careful mathematical estimation of the number of individuals 
in a given bulk of water. Presumably from this and other 
data some knowledge may be gained of the quantity of life 
which any definite area of the sea is capable of sustaining. 
Prof. Ernst Haeckel, of Jena, has lately published an 
admirable resumé of our knowledge of pelagic life, and has 
made a very distinct advance by formulating some of the laws 
which govern its distribution. He has probably done more 
than any one man to advance our knowledge on this line. 
Ever since 1854, when, as he tells us, he accompanied the 
great Johannes Müller to Heligoland and was there introduced 
by his master to the marine wonderland, he has almost con- 
tinuously pursued the study of the Plankton. He believes 
that-aquatic life in its broadest features shows conditions of 
distribution similar to those of terrestrial life, and that we may 
for the former as well as for the latter distinguish five great 
geographical provinces, each represented by characteristic 
forms of animals and plants. 1. The Arctic Ocean. 2. The 
Atlantic. 3. The Indian. 4. The Pacific. 5. The Antarctic. 
_ All aquatic organic forms fall into two great divisions. 
1. Those which live free in the water, either swimming 
actively or passively floating at the mercy of currents and 
winds. These compose the Plankton. The Plankton thus 
includes the widest range of organic size and form, from the 
minutest microscopic organisms to the gigantic cetaceans. 
2. Those forms which live upon the sea bottom, either fixed 
or creeping about. To these the term Benthos (ré f¢»40s, the 
bottom of the ocean) is applied. The variety of forms living 
near the shore is known to vary with the depth, while the 
forms characteristic of the comparatively shallow waters of 
the coasts are widely different from those which inhabit the 
bottom of the deep sea. 
The number and the kind of forms composing the Plank- 
ton are found to differ with the quality of the water, %. e. fresh 
or salt. In the ocean there is a marked difference which is 
conditioned by the distance from the shores, either of conti- 
nents or islands. There are many species of animals, particu- 
