CONCLUSION. 



" Once heave the ball from the hand, and one can show how all 

 this mighty order grew. That famous aboriginal push is propa- 

 gated through every atom, through all the races of creatures, and 

 through the history and performances of every individual." 

 EMERSON. 



THE word invisible, as applied to at least some of 

 the forms of life here treated of, and notably to the 

 Sponge, may appear to an objector as a misnomer. 

 Yet, not to be hypercritical, he might say : " I 

 understand that by this term you mean those forms 

 of life which are invisible, or nearly so, to the un- 

 assisted eye, and though not literally correct, yet 

 is sufficiently so for our ordinary every-day-life 

 mode of speaking, in which considerable latitude 

 of expression is allowed, and no misunderstanding 

 results. But to speak of a Sponge, which can be 

 readily seen, as belonging to this class of being is 

 surely erroneous." 



