SPONGES. 



45 



scribed, by which a constant stream enters at the pores, 

 and passes out at the oscida. The one is a mechanical, 

 the other a vital operation. The latter is performed only 

 during life and health, and contributes to the nourishment 

 of the animal ; the former goes on after death, and is of 

 no benefit to the Sponge, though very useful to its possessor. 

 The one may be compared to that indiscriminate devouring 

 of books, which we sometimes see in great readers — a 

 voracity insatiable indeed, but which leaves the mind as 

 empty as it was before ; the other to that guarded selec- 

 tive reading which ever watches to extract mental food, 

 separating and rejecting by a secret, but potent alchemy, 

 the useless and the bad. Or we may compare the one to 

 a soul dead in trespasses and sins, incapable (because 

 destitute of spiritual perceptions) of distinguishing truth 

 from error, and therefore carried about by every wind of 

 doctrine of those who lie in wait to deceive, — the tools of 

 Satan and his agents, whose purposes they are unconsci- 

 ously serving. The other maybe likened to a living soul, 

 who brings everything to the touchstone of the Word, 

 proving all things, and holding fast only that which is 

 good, by which he is nourished and edified, his spiritual 

 life is developed, and he grows in knowledge, in service, 

 and in grace. 



Perhaps we may carry this parallel further. The eclectic 

 process in the Sponges is not so simple a thing as might 

 be supposed. From the common water, which bathes all 

 alike, various and dissimilar substances are separated, 

 selected, and appropriated by different species. " For 

 example, it is very common to find growing on the same 

 reck, or seaweed, a siliceous, a calcareous, and a horny 



