308 THE MICROSCOPE. 



that part of Vital Principle of which plants partake; but 

 all animals appear besides it to have the sense of Touch ; 

 and we shall, hereafter, explain why each of those functions 

 has been allotted. Let it suffice, for the present, to say 

 that the Vital Principle in animals is the source of the 

 nutritive, the sentient, cogitative, and motive faculties ; 

 and that by them it has been defined." 



If we take this definition of animal life as our guide, 

 we cannot go far wrong; at all events, we shall not run 

 into the erroneous and false mode of reasoning found in 

 the Preface to British Diatomacece j page 20. The author 

 seriously tells us, that because bubbles of some kind of 

 gas are seen to be given off, under the influence of light, 

 when a mass of Diatomacece is present in the water, that 

 this gas must be oxygen. Why not carbonic acid gas or 

 hydrogen? Is it not as likely to be one as the other? 

 Has the gas been collected, and an analysis made of it ? 

 Would not any one of these gases rise as steadily through 

 water, " and float up portions of the Diatomaceous stratum 

 by the buoyancy of their globules"? 



Again, is it possible to take Diatomacece free from vege- 

 table sporules of some kind or other? What do they live 

 upon, vegetable or animal matters ? If vegetable feeders, 

 is it not more than probable, that when caught a portion 

 of vegetable food is taken home with them to our glass jars, 

 and that the gas is given off by the vegetable matters? The 

 experience of all collectors would confirm such a view, for 

 they are known to live much longer in confinement with 

 vegetable matter, growing in the water in which they are 

 placed, than when deprived of it. Entomostraca greedily 

 devour Diatomacece, ; but not the Conferva?, Algce, or other 

 plants, contained in the same water. No starch has ever 

 been shown, by the most delicate test, to enter into 

 the formation of the Diatomacece; is not this another 

 point in favour of their animal nature ? This vegetable 

 product has been detected in Desmidiacece. Many other 

 features might be urged in support of our argument, 

 but the most important of all is, the independent motile 

 power exercised by these wonderful little organisms. In 

 some beautiful specimens of Surirella and Namcula kept 

 under a ^ object-glass for several hours, their activity and 



