REPRODUCTION OP SPONGES. 563 



movement in the individual particles, of which the flesh of the 

 Sponge is composed. 



1144. The Sponges may be multiplied by artificial division ; 

 each portion then becoming a new individual, like the sepa- 

 rated buds of Plants. But no such division appears to occur 

 in their natural state ; and they are reproduced by the separa- 

 tion of minute spore-like bodies from the gelatinous portion of 

 their tissue. This process takes place, in the species of our own 

 coast, at the earlier part of winter. At that period, the little 

 reproductive bodies, or gemmules, first appear as minute opaque 

 yellow points, irregularly distributed in the substance of the 

 body, and usually at a distance from the surface. As their 

 development proceeds, they become larger and more opaque, and 

 present a regular oval form. They then protrude from the 

 gelatinous lining of the canals, into their cavity ; and it is seen 

 that the protruding portion is covered with cilia, which are in 

 active operation. After a further period, they become altogether 

 detached from the parent structure, and swim forth, by m%ans 

 of the cilia, through the large orifices in which the canals termi- 

 nate. In this condition they appear as egg-shaped particles of 

 gelatinous matter, the greater part of whose surface is covered 

 with cilia ; but the smaller end, by which they were previously 

 attached, is left bare. By the vibration of these cilia they swim 

 about for some time, very much in the manner of Animalcules. 

 Their motions are equal, smooth, and gliding ; and they appear 

 to be influenced by each others' proximity. When they 

 approach near to each other, as is sometimes observed, they often 

 arrest their course, and swim for a short time round each other. 

 They appear by these movements to seek a place adapted to 

 their development ; and to this they seem partly guided by the 

 influence of light, which they seek to avoid. The nature of the 

 site chosen varies with the species. Some incrust the surfaces 

 of loose stones or shells ; others stand erect upon a solid base ; 

 and others hang from the under surfaces of projecting rocks. 

 Sometimes earthy spicula may be observed in the gemmules, 

 before they have attached themselves ; and in those species which 

 possess them in the perfect form, they always appear within a 

 short time after they are fixed. No trace of internal canals, how- 



