EECEEATIVE SCIENCE. 



lOD 



SCIENCE ON THE SEA-SHOEE. 



II. — rHTSIOlOGY OF SPONGES. 



Having obtained a glimpse of tlie important 

 part the sponges have performed in building 

 up tbe rocky fabric of tbe world, let us take 

 note of a few facts of tlieir modern history, and 

 we sball tlien be better prepared to ascend a 

 step biglier in tbe ladder of marine zoology. It 

 must not be supposed that remains of sponges 

 are found only in flints ; cbalk also abounds 

 witb tbeir spicules. The muddy deposits now 

 forming round our coasts receive additions 

 from the sponges that now people the seas ; 

 and in the white sand of the Mediterranean 

 the remains of sponges are in regular process 

 of deposit, and in many instances these prove 

 to be almost identical with those found in 

 the flints (7). On the other hand, many fossils 

 besides those of sponges abound in flint ; 

 polypes, foraminifera, fish-scales, desmidije, 

 true shells, etc., etc., are evidences of the va- 

 rieties of life which abounded in the ancient 

 seas. Now, look at this piece of sponge 

 which I have brought with me to clean the 

 sides of our glass vessels. It is the common 

 sponge of commerce. At first sight, the 



meshes appear to be confused, but, on close 

 inspection, we can easily detect channels 

 passing through from the external wall to 

 the inner side of the cup-shaped mass. 

 Around these are numerous small pores, and 

 the universal prevalence of these pores gives 

 the family its scientific name of Porifera. 

 We know but little as to the life of the 

 sponge. It was at first a stretch of imagina- 

 tion to conceive the mass contracting and 

 dilating, and thus causing a regular flow of 

 water through the pores to the interior, and 

 by the tubes again to the exterior, the food 

 being separated for the use of the creature 

 by the straining process. This has since 

 been proved to be the mode of its living, the 

 sponge proper is the frame-work or skeleton, 

 and the gelatinous living fabric which re- 

 sides in and upon it obtains nourishment in a 

 manner similar to that of the minute ciliated 

 creatures that we delight to watch under the 

 microscope, churning the water and entrap- 

 ping all sorts of unsuspecting creatures in 

 their unscrupulous gullets. It was reserved 



Vol. I.— No. 4. 



