210 LIFE ON THE EARTH. 



of cells breaks up into smaller aggregates, or is re- 

 solved into solitary cells again, and our little circle 

 of discovery is completed. 



Given, therefore, something more; a current of 

 water guided by cilia through the mass ; removal and 

 renewal of cells; addition of a new substance to 

 line the canals, in forms determined by these cur- 

 rents ; the growth of germs capable of being sepa- 

 rated and going through the same series of events; 

 in short a sponge, for the possession of which Botany 

 and Zoology have had a long conflict, and which 

 seems placed at the very lowest limit of specific life. 



What is the next step, or rather leap, is hard to 

 say; for if we go to the minute Foraminifera, that is 

 a group of aggregated and perforated cells, with cilia, 

 which helps us very little or not at all in the advance- 

 ment of animalization ; but if we ascend per saltum 

 to the Zoophyta most allied to Spongiadse, and claim 

 affinity with Alcyonium, we require the large postu- 

 lates of freely moving polypi, with eight arms round 

 the contractile mouth, a complete digestive cavity, 

 and ova of definite character. 



Then again is another hiatus between the Alcyo- 

 nidse and the Mollusca, which neither fossil nor 

 recent life can fill; and thus in what seem to be 

 the first and easiest steps we can imagine, nothing 

 but postulate upon postulate will bring us on our 



