XXIV INTRODUCTION. 



In addition to these, there are numberless kinds of micro- 

 scopic animalcules, commonly called infusory animals (Infu- 

 soria), from their being found specially abundant in water 

 infused with vegetable matter. Indeed, a great many that 

 were formerly supposed to be animals are now known to be 

 vegetables. Others are ascertained to be crabs, mollusks, 

 worms, &c. in their earliest stages of development. In 

 general, however, they are exceedingly minute, exhibiting 

 the simplest forms of animal life, and are now grouped 

 together, under the title of Protozoa. But, as they are still 

 very imperfectly understood, notwithstanding the beautiful 

 researches already published on this subject, and as most of 

 them are likely to be finally distributed among vegetables 

 and various classes of the animal kingdom, we have not 

 assigned any special place to them. 



