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 he 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 

 grow superficially from a solid base, some penetrate like de- 

 structive parasites into the texture of other animals. Thus the 



