650 



niOTOZOA. 



sponuy incrustation; whilst others shoot up a branched stem into the water; and others again 

 hanir t'reolv tVoni the sca-wcods float iui;- in the ocean. Many sponges are remarkable for 

 the singularity of thcli' forms, sometimes spreading into broad leaves or fans; sometimes 



they are cyliiulrieal like a thick stick ; 

 now assuming the form of a hand, and often 

 liollowed out in the shape of a cup, with a 

 foot like a vase. They occur abundantly on 

 all shores from Greenland to Australia, but 

 are most numerous and gigantic in hot lati- 

 tudes. The common sponge of commerce 

 is chiefly found in the Mediterranean, where, 

 especially among the beautiful Isles of Greece, 

 an important fishery and traffic are carried 

 on for this article. " At the Cycladcs, for 

 instance, sponge-diving forms the chief em- 

 ployment of the population. The sea is at 

 all times exceedingly clear, and the experi- 

 enced divers are able to distinguish from 

 the surface the points to wdiich the Sponge 

 is attached below, when an unpractised eye 

 could but dimly discover the bottom. Each 

 boat is furnished with a large stone attached 

 to a rope, and this the diver seizes in his liand 

 on plunging head foremost from the stern. He 

 does this in order to increase the velocity of 

 descent, thus economizing his stock of breath ; as well as to facilitate his ascent when exhausted 

 at the bottom, being then quickly hauled up by his companions. Few men can remain longer 

 than two minutes below ; and as the process of detaching the sponge is tedious, three and some- 

 times four divers descend successively to secure a particularly fine specimen." This fishery 

 appears to have been prosecuted in the same locality in very ancient times. Tournefort states 

 that of so much importance is it considered in the region where it is carried on, that no youth is 

 allowed to marry until he has given proof of his proficiency in the art of diving. 



^ri:^ 



THE COMMON SPONGE. 



€la§s III. RHIZOPOI>A. 



In the deposit formed at the bottom of fresh-water ponds, we may often meet with a singular 

 minute gelatinous body, which constantly changes its form even under our eyes, and moves 

 about m its native element bj^ means of finger-like processes, which it appears to have the 

 power of shooting out from any part of its substance. This shapeless gelatinous mass is an 

 animal, the Amoeba diffluens, well known to microscopic observers under the name of the Proteus, 

 from the continual changes of shape which it presents to our notice. (See engraving, p. G46.) It 

 consists entirely of the granular gelatinous matter already mentioned as sarcode, and appears to be 

 nearly homogeneous in its texture ; that is to sav, the outer surface exhibits no signs of being 

 bounded by any distinct membrane or laj^er of a firmer consistence than the rest of the body. 



No indications of any internal organization are to be recognized in this creature ; for it pos- 

 sesses neither mouth nor intestinal canal. It is not to be supposed, however, that the animal 

 keeps a perpetual fast, or that its food is entirely of a fluid nature. On the contrary, it appears 

 to be, in its small way, of an exceedingly voracious disposition, seizing upon any minute aquatic 

 animals or plants that may come in its path, and appropriating them to the nutrition of its own 

 gelatinous person. 



