PORIFERA. 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 : " All these things live and remain for ever for all uses j 

 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 f ' 



PORIFERA.. 



SPONGES.* 



THE term Porifera, or Canal-bearing 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 sponge, showing siliceous spicula imbedded in a soft matrix. 2. 

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

 rings of growth, and a portion of horny fibre, enclosing a bundle of spicula of the genus 

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

 Canada balsam, showing the spicula more plainly. 6. Tricuspid-anchorate spicula, 

 sphero-stellate. 7. Acuate-biclavate, double recurvo-ternate, expando^ternate, detri- 

 radiate spicula. 8. Gemmules of- Ckodia. 9. Gemmules of Spongilla fluviatilis 

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

 ofGeodia in an advanced stage of growth. 12. Birotulate spicula from the Fluviatilis. 

 13. Gemmules of Spongilla fluviatilis immersed in acid, to show its coating of birotu- 

 late spicula. 



N 



