562 NUTRITION AND GROWTH OF SPONGE. 



cut with sharp instruments, pierced with red-hot wires, or torn 

 into fragments ; and yet no change of form, or rather evidence 

 of sensibility, can be perceived in them. The parts which are 

 unimpaired will continue to present the same phenomena as be- 

 fore ; and no injury seems to have any influence, beyond the por- 

 tion immediately affected by it. Nevertheless some observers 

 maintain that a shock, affecting the whole mass alike, does pro- 

 duce an evident effect upon it. This has been particularly noticed 

 in the Spongilla, or River-sponge. When allowed to fall into 

 water from the height of a few inches, or when the stage of the 

 miscroscope is struck, the tubular prolongations on which the 

 vents are situated contract very sensibly, until the orifice is 

 nearly closed, and projects but slightly. It has also been 

 noticed that these projecting orifices vary considerably in their 

 form at different times, even within short intervals, and when 

 no external cause has influenced them. Some Naturalists state, 

 moreover, that, although no sensible contractions and dilatations 

 can be seen in the whole mass, a peculiar sensation is felt when 

 the hand is placed upon a specimen still under water. This 

 sensation is of a tingling character, and appears due to some 

 movement in the individual particles of which the flesh of the 

 Sponge is composed. 



1229. The Sponges may be multiplied by artificial division 5 

 each portion then becoming a new individual, like the separated 

 buds of Plants. But no such division appears to occur in their 

 natural state ; and they are reproduced by the separation 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 



