THE LOWER FORMS OF LIFE. 65 



from fatigue, without having seen the torrent for one instant change 

 its direction, or dimmish in the slightest degree the rapidity of its 

 course." 



I have said that in this efferent fountain the germs of the Sponge 

 were emitted. Let us take up one of these tiny creatures and 

 follow out its life history. 



This germ, or gemmule, is essentially a Protozoon. It is a cell 

 formed of sarcode. If you look attentively through a lens you will 

 observe that the efferent fountain of water will propel this little 

 germ to a considerable distance, where you would, a priori, imagine 

 that it would be left to sink to the bottom. No such thing. You 

 will find that, beyond the influence of the fountain of water, it has 

 the power of motion, and, if you examine it attentively, you will 

 find that this is due to a series of delicate cilia attached to the 

 posterior part of the cell, just as we observed in the bell of 

 Vorticella. This Sponge germ is an independent atom of living 

 matter, and it moves through the water propelled by a will prescient 

 of its future destiny among living things. 



At length this little germ finds a resting place, which, when once 

 found, is, like that of the Vorticella or the oyster, its locality for 

 life. This is either a shell, a stone, a rock, or some solid substance 

 in the water. When it touches such a substance it becomes attached 

 to it by its ciliated extremity, and then flattens itself out into a thin 

 disc, well shown in Fig. 81. Now it is seldom that very small 



Fig. 81. Three sponge gemmules fixed to a rock and spread out The spiculse are seen 

 being developed. There were three more on the rock from which Mr Bowerbank's plate 

 was taken, all of which would have united together, forming one Sponge. 



sponges of the larger species are found, and this arises from the 

 fact that a number of other germs fix themselves to the same foun- 

 dation, and they then join together and grow up as one Sponge, as 

 the figures in the cut would have done had they not been taken out 

 of the water. Well, this delicate, thin, flattened-out film of sarcode 

 would be a most agreeable bonne louche for the numerous predatory 

 inhabitants of the sea, and more particularly would it be liable to 

 the insinuating attacks of small Annelids. But, to compensate for 

 this danger, the Sponge is endowed with the power of forming a 

 most remarkable series of flinty or chalky spiculse, which, among 



F 



