68 



PORIFERA. 



sented : " On moving the watch-glass, so as 

 to bring one of the apertures on the side of 

 the sponge fully into view, I beheld, for the 

 first time, the splendid spectacle of this living 

 fountain, vomiting forth from a circular cavity 

 an impetuous torrent of liquid matter, and 

 hurling along in rapid succession, opaque 

 masses, which it strewed every where around. 

 The beauty and novelty of such a scene in 

 the animal kingdom, long arrested my atten- 

 tion ; but after twenty -five minutes of constant 

 observation 1 was obliged to withdraw my 

 eye, from fat'gue, without having seen the tor- 

 rent, for one instant, change its direction, or 

 diminish, in the slightest degree, the rapidity 

 of its course; I continued to watch the saute 

 orifice, at short intervals, for five hours, some- 

 times observing it for a quarter of an hour at 

 a time, but still the stream rolled on with a 

 constant and equal velocity. About the end 

 of this time, however, I observed the current 

 become perceptibly languid ; the opaque floc- 

 culi of feculent matter, which were thrown 

 out with so much impetuosity at the begin- 

 ning, were now propelled to a shorter dis- 

 tance from the orifice, and fell to the bottom 

 of the fluid within the sphere of vision, and, 

 in one hour more, the current had entirely 

 ceased." 



Subsequently, two round portions of the 

 Spongia panicea were placed together in a 

 vessel of sea-water, with their orifices opposite 

 to each other, at the distance of two inches ; 

 they appeared to the naked eye like two living 

 batteries, and soon covered each other with 

 feculent matter. Dr. Grant then placed one 

 of them in a shallow vessel, and just covered 

 its surface and highest orifice with water. 

 On strewing some powdered chalk on the 

 surface of the water, the currents were visible 

 at a great distance, and on placing some small 

 pieces of cork or of dry paper over the aper- 

 tures, he could perceive them moving by the 

 force of the currents at the distance of ten 

 feet from the table on which the specimen 

 rested. A portion of soft bread pressed be- 

 tween the fingers into a globular form was not 

 moved away in a mass by the stream, but was 

 gradually worn down by the current beating 

 on its sides, and thus propelled to a distance 

 in small flakes. A globule of mercury of 

 equal diameter with the orifice, let fall upon 

 it from a glass tube, was not removed or 

 shaken, and completely stopped the current. 

 In this condition, on piercing the sponge with 

 a needle, a new current was established through 

 the artificial canal thus formed, which con- 

 tinued even after removing the obstruction 

 from the original orifice. 



A globule of mercury of any smallness 

 placed over the orifice of a living sponge, is 

 too heavy to be affected by the small column 

 of water which impels against its smooth 

 round surface, flowing at the rate with which 

 it issues from that orifice, and is useful in 

 enabling us to stop up the currents of certain 

 orifices, in order to direct the stream with 

 greater force through a particular aperture 

 which we wish to examine through the mi- 



croscope. By adopting this plan with some 

 sponges, which have very few and large 

 orifices on the surface, it is distinctly per- 

 ceptible with the naked eye, that the current 

 never enters by the same apertures through 

 which it issues, and we might thus measure 

 the whole strength of the forces employed to 

 produce the currents in any particular speci- 

 men.* 



Various hypotheses have been suggested to 

 account for the production of these streams of 

 water which constantly percolate the body of 

 the sponge, but all of them have been rejected 

 in turn as unsatisfactory. Ciliary movement 

 might be supposed to be the cause of this 

 phenomenon, were it not that no observer 

 has been able to detect, even with the most 

 powerful microscopes, the presence of cilia in 

 the interior of the aquiferous canals. At 

 certain seasons, indeed, when the ciliated re- 

 productive gemmules described by Dr. Grant 

 are abundantly disseminated through the living 

 cortex of the sponge, it would seem possible 

 that they might have some influence ; but as 

 the currents appear to be equally strong at 

 all periods, even when these gemmules are 

 not developed, this supposition is untenable. 

 Lastly, the laws of endesmosis have been ap- 

 pealed to as capable of explaining the phe- 

 nomenon in question, yet even here there are 

 difficulties not easily got rid of. 



In speaking of this propulsion of the sea- 

 water through the Halichondria, in which 

 genus it has been principally observed, the 

 crustaceous species being best adapted for the 

 study of its phenomena, Dr. Johnston re- 

 marks f, "A single observation is sufficient 

 to convince us that this circulation has no- 

 thing in common with that of higher animals, 

 but it has some analogy surely with that 

 imbibition and influx of water into the body 

 of most radiated and molluscous animals 

 which takes place through the skin and through 

 certain canals, which Delia Chiage has de- 

 scribed and figured as their aquiferous system. 

 The canals in both cases are not vascular tubes 

 with membranous parietes, but rather fur- 

 rows, excavated in the flesh or substance of 

 the body, and leading into wider channels 

 equally unlined. They have in common a direct 

 communication with the circumfluent water, 

 which alone ever flows in them, and the en- 

 trance of this water seems to be, in a great 

 measure, or entirely, independent of the will 

 of the animals ; but the polypes and mollusca 

 only have the power of expelling it when they 

 choose by the contraction and compression of 

 the parts which the canals traverse. There is, 

 however, a wider difference in the arrangement 

 of the aqueducts, in the Radiata and Mol- 

 lusca, the pattern is the same in every in- 

 dividual of each species, but in the Sponges 

 it has no constancy, so that in no two 

 specimens of the same kind do we ever find 

 the arrangement to be exactly alike. 



This inconstancy seems to prove that the 



* Edin. Phil. Journal, vol. xiii. p. 104. 

 f Hist, of British Sponges, p. 89. 



