INTRODUCTION. 19 



vitality, spontaneously detach themselves and evolve into 

 similar fabrics elsewhere. 



It is, however, amongst the algae that vegetable and 

 animal life appear to be the most completely blended to- 

 gether. It is well known to naturalists that the spores of 

 some of our common fresh water algae, as for instance, con- 

 ferva glomerata and prolifera rivularis, when first dis- 

 charged into the water, move about by means of certain 

 ciliary appendages during a certain period of their life. At 

 this stage of development they were observed by Ehren- 

 berg, and were actually figured by him as infusoria. After 

 awhile, however, their cilise are absorbed, their motions 

 cease, ' they become attached to some substance in the 

 stream, and develop into plants fixed and immovable , ex- 

 cept from the influence of the current. It would appear 

 from this, that these simple unicellular organisms are 

 animals during the first period of their life and vegetables 

 towards its close. 



All organized matter, whether animal or vegetable, con- 

 sists of cells, and life is only known to us as manifested 

 through their agency. Not only may every animal and 

 plant be traced to a simple cell, but organic nature is evi- 

 dently only a series of forms which exhibit the successive 

 stages of its development. The animal and plant seem to be 

 blended together in this the primitive form of all organized 

 being. It is here that the last signs of animality disappear, 

 after which, life becomes wholly vegetative. 



It is not then among vegetables and animals the most 

 highly organized, that we find the most striking analogies 

 between the animal and vegetable kingdoms, but it is those 

 which possess the greatest amount of structural simplicity, 

 that approximate the most closely to an identity of function. 



The assemblage of organized beings denominated animals 



