How Do Sponges Grow?
In their growth, some sponges assume a determinate figure or at least one whose variations are confined within certain limits. The greater number are irregular and variable, their shape depending in a great measure upon the peculiarities of their state, to which they easily accommodate themselves. They will incrust a shell, or a crab, a rock, or seaweed, following every projection and sinuosity. The offshoots will spring up with a more luxuriant growth in the deeper sheltered places until the original shape of the foundation they grow upon is lost to sight.
Sponges are unmoving and inirritable. They never remain rooted to the places of the germination, and are incapable either of contracting or dilating themselves or even of moving any fiber or portion of their mass. The functions which distinguish them as living beings are few, and faintly imaged.