A SUBAQUEOUS CITY. 147 



of life a kind of " subaqueous city " (as Pro- 

 fessor Huxley terms it), yet differing from all 

 other cities in this, that they themselves are at 

 once the inhabitants and the city -like structure. 



This Sponge city, like most other cities of 

 commercial importance, is built on the banks of 

 a river, which intersects and permeates its every 

 part, bringing food, and all the requisites of 

 health and prosperity to the inhabitants. These 

 latter build themselves into over-arching passages 

 and grottoes throughout its entire length and 

 breadth, living on and over the river, drinking 

 in its life-giving element, and so completely identi- 

 fying themselves with it as to make its currents 

 perform the life functions of circulation and re- 

 spiration analogous to that obtainable by a more 

 complex method in the higher animals. So the 

 river and the Sponge go together in Sponge life ; 

 for, while the water external to the Sponge is not 

 dependent on the Sponge, its form and motion as 

 a river or running stream through the Sponge 

 city is produced by the latter, and may, in this 

 sense, be said to be so. Yet the Sponge itself is 

 absolutely and entirely helpless without the former 



