388 THE INHABITANTS OF THE SEA. 
size, they are gradually clothed with vibratile cilia, and, finally 
detaching themselves, are cast out through the oscula into the 
world of waters. Here their wanderings continue for a short 
time, until, if they be not devoured on the way, they reach some 
rock or submarine body on which, tired of their brief erratic 
existence, they fix themselves for ever, and, bidding adieu to all 
further rambles, lead henceforth the quiet sedentary life of their 
parents. In this manner the sponges, which otherwise would 
have been confined to narrow limits, spread like a living carpet 
over the bottom of the seas, and in spite of their being utterly 
defenceless, maintain their existence from age to age. At the 
same time they serve to feed a vast number of other marine 
animals, for the waters frequently swarm with their eggs, and 
these afford many a welcome repast to myriads of sessile molluscs, 
annelides, polyps, and other creatures small or abstemious 
enough to be satisfied with feasting on atoms. 
Sponges inhabit every sea and shore, and differ very much in 
habit of growth. For whilst some can only be obtained by 
dredging at considerable depths, others live near the surface, 
and others, again, attach themselves to the surfaces of rocks and 
shells between the tide marks. Like the corals, they revel in 
every variety of shape and tint, imitate like them every form 
of vegetation, and adorn like them the submarine grounds with 
their fantastic shrubberies. The fine collection of West Indian 
sponges exhibited in the Crystal Palace, but to which fancy 
must add the additional ornament of colour, may serve to give 
some idea of their prodigal versatility of growth. More than 
sixty different species have been discovered in the British waters 
alone, and as they go on increasing iu numbers, size, and beauty, 
until they attain their highest development along the shores of the 
tropical ocean, they no doubt hold a conspicuous rank among 
the living wonders of the sea. The branched sponges, with a 
compact feltred tissue, are more common than others in the colder 
maritime domains, where the species of a loose texture, which 
grow in large massive forms, either do not exist or are very rare. 
Many sponges are of considerable size, such as the vase-like 
tropical species known under the name of Neptune’s cup; others 
are almost microscopical; and while by far the greater number 
erow superficially from a solid base, some penetrate like de- 
structive parasites into the texture of other animals. Thus the 
