Their antennae and swimming organs are immeasurably prolonged in the darkness.

The filaments of their body, long hairs rich in nerve terminals, can distinguish instantaneously the appetizing prey, or the enemy lying in wait.
The abyssal deeps have two floors or roofs.

In the highest, is the so-called neritic zone,--the oceanic surface, diaphanous and luminous, far from any coast.

Next is seen the pelagic zone, much deeper, in which reside the fishes of incessant motion, capable of living without reposing on the bottom.
The corpses of the neritic animals and of those that swim between the two waters are the direct or indirect sustenance of the abyssal fauna.
These beings with weak dental equipment and sluggish speed, badly armed for the conquest of living prey, nourish themselves with the dropping of this rain of alimentary material.

The great swimmers, supplied with formidable mandibles and immense and elastic stomachs, prefer the fortunes of war, the pursuit of living prey, and devour,--as the carnivorous devour the herbivorous on land,--all the little feeders on debris and _plancton_.