. Animal life as affected by the natural conditions of existence. Animal ecology. 342 THE INFLUENCE OF LIVING stream of water, produced by the cells of the sponge, cir- culates through the system of tubes thus formed, and this, it would seem, supplies the animal with food, consisting of micro- scopic organisms. By a course of growth and subdivision, aftei' the manner of plant-growth, a compound sponge is fre- quently formed; one, that is to say, which has a number of mouths, more or less, and in which the centi'al cavity—which in calcareous sponges is often quite simple—is trans
. Animal life as affected by the natural conditions of existence. Animal ecology. 342 THE INFLUENCE OF LIVING stream of water, produced by the cells of the sponge, cir- culates through the system of tubes thus formed, and this, it would seem, supplies the animal with food, consisting of micro- scopic organisms. By a course of growth and subdivision, aftei' the manner of plant-growth, a compound sponge is fre- quently formed; one, that is to say, which has a number of mouths, more or less, and in which the centi'al cavity—which in calcareous sponges is often quite simple—is transformed into a highly complex structure of internal canals and cavities. These soft and perfectly harmless organisms, sometimes, how-. FlG. 91.—a. longitudinal section throuph a calcareous sponge, showing its simple central cavity. 6, the sponge uninjiured. (From HaeckeL) ever, growing to an extraordinary size, offer a welcome shelter in their inniimerable cavities to a host of other creatures, which retire into them, as I might say, for rest and refreshment, and cin easily find in their labyrinthine passages a j^lace of con- cealment from the pursuit of their enemies; sometimes these are true parasites, sometimes only commensals, which establish themselves there. Such a specimen of sponge freshly dredged up from the sea ofiers to the collector a rich mine of Annelids aad Planarians, Nemertidse and Polypes; Crabs of every kind, various Mollusca, and even Fishes, may be found, and Plants,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Semper, C. (Carl), 1832-1893. New York, D. Appleton
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