KIDD'S OWN JOURNAL. 



291 





netted mass, commensurate with the size of 

 the whole Sponge. The horny Sponges are 

 almost confined to the warmer seas, but the 

 siliceous and calcareous kinds are common 

 with us ; especially the former. 



The solid parts are, during life, invested with 

 a glairy transparent slime, so fluid in most 

 species as to run off when the Sponge is 

 taken out of its native element ; yet this 

 clear slime is the flesh of the animal. 



The spicula, whether of flint or lime, or the 

 horny fibres, are so arranged as to form num- 

 berless pores, with which the whole animal 

 is perforated ; it is to these that our common 

 Sponge owes its most valuable property of 

 imbibing and retaining water, as we shall 

 presently see when we investigate the history 

 of this species in detail. In life, the sur- 

 rounding water is made to flow through these 

 pores by a continual current*(interrupted, 

 however, at the will of the animal) from with- 

 out into the interior of the body. But 

 whither goes this current ? The pores lead 

 into large channels, which also run through 

 the body, like the drains from individual 

 houses, which run into the main sewer ; and 

 these open on the exterior of the body, by 

 more or less conspicuous orifices called oscala, 

 or mouths. From these latter the effete 

 water is poured in forcible streams, and thus 

 a circulating current is maintained. 



It was Dr. Grant who first established the 

 fact of this current from personal observa- 

 tion. His account of the discovery is full 

 of interest. " I put a small branch," he ob- 

 serves, " of the Spongia coalita, with some 

 sea-water, into a watch-glass, under the 

 microscope ; and, on moving the watch-glass 

 so as to bring one of the apertures on the 

 side of the Sponge fully into view, I behold, 

 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 everywhere 

 around. The beauty and novelty of such a 

 scene in the animal kingdom long arrested 

 my attention ; but after twenty-five minutes 

 of constant observation I was obliged to with- 

 draw my eye, from fatigue, without having 

 seen the torrent for one instant change its 

 direction, or diminish in the slightest degree 

 the rapidity of its course. I continued to 

 watch the same orifice, at short intervals, for 

 five hours, — sometimes observing it for a 

 quarter of an hour at a time, — but still the 

 stream rolled on with a constant and equal 

 velocity. 11 The vehemence of the current 

 then began to diminish, and in about an hour 

 ceased." 



No one can have looked with any attention 

 at the rocks on any part of our shores that 

 are left exposed by the sea at low spring- tide, 

 without noticing irregular masses of yellow 



fleshy substance incrusting them, which rise 

 into little conical hillocks perforated at the 

 extremity, like the crater-cones of tiny vol- 

 canoes. This is the Crumb-of-bread Sponge 

 (Halichondria panicea), one of our most com- 

 mon species ; and it is peculiarly suitable for 

 displaying the currents of which we have 

 been speaking. Ur. Grant remarks that it 

 presents the strongest current which he had 

 seen. "Two entire round portions of this 

 sponge," he says, "were placed together in 

 a glass of sea-water, with their orifices oppo- 

 site 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. I placed one of them 

 in a shallow vessel, and just covered its sur- 

 face 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 a dry paper over the aper- 

 tures, I could perceive them moving by the 

 force of the current, at the distance of ten 

 feet from the table ou which the specimen 

 rested. 



The publication of these facts convinced 

 naturalists that the gelatinous flesh of the 

 Sponge exerted some vigorous action by 

 which the currents were maintained, and cilia 

 were suspected to be the organs. But the 

 closest scrutiny failed to detect them, until 

 first Dr. Dobie, and then Mr. Bowerbank, 

 succeeded in seeing them in action in a living 

 native Sponge. In similar situations to those 

 where the Crumb-of-bread Sponge occurs, 

 may be found, but much more rarely, the ele- 

 gant Sack Sponge (Grantia cornpressa). It 

 takes the form of a little flattened bag of 

 angular outline, and of a whitish hue, with an 

 orifice at each angle. The bags, which are 

 frequently clustered, hang by a slender base 

 from the stalks of sea-weeds, or from the 

 naked rocks. When examined they are 

 found to be hollow, with thin walls ; and if 

 a small portion be torn off, and placed be- 

 neath a microscope, it will exhibit well the 

 structure of a spicular Sponge. The sub- 

 stance will appear crowded, and almost com- 

 posed of calcareous crystals, most of which 

 are stars of three radiating points ; but some 

 are linear needles, and on the exterior are 

 many which are pointed at one end, and ter- 

 minate in a bent, club-like knob at the other. 



It was this species which, under Mr. Bow- 

 erbank's experienced eye and delicate mani- 

 pulation, revealed the moving cilia. By 

 tearing specimens in pieces (for the use of the 

 keenest cutting instruments so crushed the 

 texture as to destroy the parts), and ex- 

 amining the separated edges with high 

 powers, he found that the sides are composed 

 of a number of hexagonal cells, defined by the 

 peculiar arrangement of the triradiate spicula, 



