Page images
PDF
EPUB

MARINE SPONGES.

307

where they grow so well that they form masses as big as a man's head. But some of them are not attractive-looking creatures; and, indeed, few people would imagine them to be animals at all. The spongy object which we know as sponge, is only the inner skeleton; just as coral is of another class of marine animals when alive. This substance is covered all over with a transparent gelatinous flesh, called sarcode, which lines every pore and every aperture. In and out of these currents of sea water perpetually flow, induced by the action of the eyelash-like processes (cilia) with which the surface of the flesh lining such hollows is covered. Among them we have the "crumb-of-bread" sponge (Halichondria panicea, Fig. 238), the Chalina oculata, Fig. 239 (largest of our British sponges), the Leucosalenia, Tethea, Grantia, Hymeniacidon, Cliona - the latter is really a boring sponge, and burrows the holes we may see covering the surfaces of old oyster-shells. Some of these sponges are of a brilliant yellow or crimson colour, and mat the surfaces of rockwork, &c., having been introduced into the sea water as "gemmules," and developed by circumstances into their present attractive and useful conditions.

No doubt the marine aquarium might be converted into a nursery for microscopic objects as well as the fresh water. There is no end to the variety of the lower forms of life inhabiting the sea. They are the oldest of all the animal kingdom, having been in

existence since perhaps before the distant Laurentian epoch of which geology speaks. They have expe

rienced all the changes which we know the ocean beds must have experienced-have repeatedly witnessed the conversion of continent into sea, and

[merged small][graphic][ocr errors]

"Crumb-of-bread" Sponge (Halichondria panicea).

ocean floor into dry land and even mountain chain. The mineral remains of some of the ancestors of living forms have taken an active part in the building up of rock masses of every geological period. We cannot wonder, therefore, that the number of species of these early and unpretending forms of life should

[subsumed][merged small][merged small][merged small][graphic]

be so great, or that they should enjoy so Cosmopolitan a distribution. There is no reason why more naturalists should not cultivate the humblest as well as the most highly-developed types of marine life, and keep living marine diatoms, foraminiferæ, noctilucæ, and sponges. Our rock-pools support them, and it is a sad proof of how little we yet know of the natural conditions of such little spots as these, if we cannot keep them artificially alive also.

That aquaria are still in the infancy of their development we do not doubt, any more than that they will administer to the growing love of animated nature which is the especial feature of the intellectual culture of our century. Here will have to be fought out and hunted down many of the embryological questions to which deep philosophical inquiry is now attaching such great importance. And, whilst aquaria may in this manner be useful to true science, they will not be less so to unscientific people, in revealing to them at a glance the shapes, habits, and natures of creatures they had never heard of before, so as thus to form a practical education all the more valuable because those who learn are for the time unaware of its importance.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small]
« EelmineJätka »