PORIFERA. 



15 



convenient method of seeing them is simply to scrape off a few 

 particles from the incinerated sponge upon a piece of glass, which, 

 when placed under the microscope, may be examined with ordinary 

 powers. 



(17.) On placing a living sponge of small size in a watch-glass or 

 small glass trough filled with sea-water, and watching it attentively, 

 something like a vital action becomes apparent.* The entire 

 surface is seen to be perforated by innumerable pores and aper- 

 tures, some exceedingly minute, opening on every part of its peri- 

 phery ; others of larger dimensions, placed at intervals, and gene- 

 rally 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 con- 

 tinual influx and efflux of the surrounding fluid is produced by an 

 agency not yet discovered, as no contraction of the walls of the 

 canals, or other cause to which the movement may be referred, has 

 ever been detected ; we are as- 

 sured, however, that it is from 

 the currents, thus continually 

 permeating every portion of 

 its substance, that the general 

 mass is nourished. The annex- 

 ed diagram, fig. 2 a, will give 

 the reader an idea of the most 

 usual direction of the streams : 

 the entering fluid rushes in at 

 the countless pores which occu- 

 py the body of the sponge ; 

 but, in its progress through the 

 canals in the interior, becomes 

 directed into more capacious 

 channels, communicating with 

 the prominent larger orifices, through which it is ultimately ejected 

 in equable and ceaseless currents. Organized particles, which ne- 

 cessarily abound in the water of the ocean, are thus introduced 

 into the sponge on all sides, and are probably employed as nutri- 

 ment, whilst the superfluous or effete matter is continually cast 

 out with the issuing streams as they rush through the fecal ori- 

 fices. The growth of the sponge is thus provided for, the living 



* Dr. Grant, in the New Edinburgh Philosophical Journal, 1827. 



