12 THE BRITISH SPONGES. 



daries were too distinctly draAvn to admit of any debateable 

 acres on either side. 



Sponges are inimoving and unirri table : hence they ever 

 remain rooted to the places of their germination, and are 

 incapable either of contracting or dilating themselves, or 

 even of moAang any fibre or portion of their mass. They 

 jiossess no polypous tenantry, — their osculi and pores are 

 unfm-nished with tentacula, — and their interior is equally 

 A acant of the simplest viscera which are found adumbrat- 

 ed at least in all other animated entities. Of such unform- 

 ed and insensate productions we naturally presume that the 

 functions which distingaiish them as living beings must 

 be few and faintly imaged ; and notwithstanding the at- 

 tention paid of late to the subject, we find that considerable 

 obscurity hangs over their physiology. 



It has been already shown that the sm^face of the sponge 

 is everywhere porous, and that its interior is permeated 

 with irregular sinuous canals which open externally by ori- 

 fices much larger than the pores. The common belief had 

 been that the sponge had the power of sucking in the cir- 

 cumfluent water through these larger orifices, and of throw- 

 ing it out again from the same orifices, after some detention 

 of it in the canals and meshes. The current was an inter- 

 mittent one with an alternate ebb and flow.* — Of late the 

 prevalent theory has been that the water is insensibly ab- 

 sorbed by the pores and enters the interior net-work, pene- 

 trating to every point and carrying -with it nutriment and 

 air : thence it is forced into the canals, along wliich it rmis in 

 a continuous stream that finds its issue' from the body at the 

 larger orifices or oscrda. (Fig. 6.) By this eflluent stream 



* " Spongia — foraminibu? rcspirat nquam." — Lin. Syst Nat. p. 1296. 



