PORIPERA. 177 



themselves become the food of larger Infusoria, and of numerous other 

 small animals, which in their turn are devoured by larger animals ; 

 and thus a food, fit for the nourishment of the highest organised beings, 

 is brought back, by a short route, from the extremity of the realms of 

 organised matter. These invisible animalcules may be compared, in 

 the great organic world, to the minute capillaries in the microcosm of 

 the animal body ; receiving organic matter in its state of minutest sub- 

 division, and when in full career to escape from the organic system, 

 turning it back, by a new route, towards the central and highest 

 point of that system." 



Such, then, seem to be some of the purposes for which are created 

 the wonderful invisible myriads of infusorial animalcules. In the words 

 of Holy Writ : " AU these things live and remain for ever for all uses ; 

 and they are all obedient. All things are double one against another ; 

 and He hath made nothing imperfect. One thing establisheth the 

 good of another ; and who shall be filled with beholding His glory ?" 



POEIFERA. 



SPONGES.* 



The term Porifera, or Canal-hearing Zoophytes, was applied by Pro- 

 fessor Grant to designate the remarkable class of organised beings 

 usually known as sponges, which are met with in most seas, growing 

 in great abundance on the surface of rocks. 



Ellis, in the course of his investigations, was astounded by disco- 

 vering that sponges possessed a system of pores and vessels, in which 

 sea-water passed, with all the appearance of the regular circulation of 

 fluids in animal bodies, and a seeming purpose of conveying animal- 

 cules to the animal for food. Professor Owen gives it as his opinion 



* Description of Plate IV. 



1. Portion of gpoDge, showing siliceous spioula imbedded in a soft matrii. 2. 

 Skeleton of sponges of the aoerate form, covered with rows of spines. 3. Showing 

 rings of growth, and a portion of homy fibre, enclosing a bundle of spioula of the genus 

 Verongia. 4. Sphero-stellate spicula of TetJiea. 5. Portion of sponge mounted in 

 Canada balsam, showing the spioula more plainly. 6. Tiiouspid-^nchorate spioula, 

 Bphero-steUate. 7. Aouate-biolavate, double reourvo-ternate, expaido-t^ernate, detri- 

 radiate spioula. 8. Gemmules of Geodia. 9. Gemmides of Spongilla Jlumatilu 

 enclosed in spioula. 10. Clavate spicula, covered with short spines. 11. Gemmules 

 of Geodia in an advanced stage of growth. 12. Birotulate spioula from the Fluviatilis. 

 13. Gemmulesof/Spcm^»Ho/««tafa7M immersed in acid, to shew its coating of birotu- 

 late spicula. 



