SPONGIA OFFICINALIS. 



at intervals, and generally elevated upon prominent portions 

 of the sponge. Through the smaller orifices the surrounding 

 water is continually sucked, as it were, into the interior of the 

 spongy mass, and it as constantly flows out in continuous 

 streams through the larger openings. This continual influx 

 and efflux of the surrounding fluid is produced by an agency 

 not yet discovered, as no contraction of the walls of the ca- 

 nals, or other cause to which the movement may be referred, 

 has ever been detected. It is certain, however, that it is from 

 the currents thus continually permeating every portion of its 

 substance, that the general mass is nourished. The diagram, 

 Plate I. Fig. 2, a, will give an idea of the most usual direc- 

 tion of the streams ; the entering fluid rushes in at the count- 

 less pores which occupy the body of the sponge, but, in its 

 progress through the canals in the interior, becomes directed 

 into more capacious channels, communicating with the prom- 

 inent larger orifices, through which it is ultimately ejected in 

 equable and ceaseless currents. Organized particles, which 

 necessarily abound in the water of the ocean, are thus intro- 

 duced into the sponge on all sides, and are probably employed 

 as nutriment, whilst the superfluous or effete matter is con- 

 tinually cast out with the issuing streams as they rush through 

 the fecal orifices. The growth of the sponge is thus provided 

 for, the living gelatinous portion continually accumulates, 

 and, as it spreads in every direction, secretes and deposits, in 

 the form peculiar to its species, the fibrous material and earthy 

 spicula which characterize the skeleton. 



From this description of the structure of a sponge, it will 

 be apparent that all parts of the mass are similarly organized ; 

 a necessary consequence will be, that each part is able to carry 

 on, independently of the rest, those functions needful for ex- 

 istence. If, therefore, a sponge be mechanically divided into 

 several pieces, every portion becomes a distinct animal. 



The multiplication of sponges, however, is effected in an- 

 other manner, which is the ordinary mode of their reproduc- 

 tion, and forms a very interesting portion of their history. At 

 certain seasons of the year, if a living sponge be cut to pieces, 

 the channels in its interior are found to have their walls stud- 

 ded with yellowish gelatinous granules developed in the liv- 

 ing parenchyma which lines them. These granules are the 

 germs or gemmules from which a future race will spring ; 

 they seem to be formed indifferently in all parts of the mass, 



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