Vlll PREFACE. 



and the methods by which they may be 

 cultivated. 



This remark is especially applicable to 

 the lower classes of animals, to the Inverte- 

 brata, and to these I have devoted the fol- 

 lowing pages. Their investigation in a 

 practical point of view has led, and will still 

 lead, to very profitable and interesting results. 

 It has been rendered more interesting of late 

 years by numerous experiments, having for 

 object the culture and artificial propagation 

 of several of the more valuable species. 



It is not sufficient to know that such an 

 insect or such a polype is utilized for certain 

 purposes in the Arts and Manufactures, we 

 must acquire at the same time a correct idea 

 of the animal itself, and the position it occu- 

 pies in the animal kingdom ; moreover, we 

 must ascertain by experiment whether any 

 species already valuable in its natural state 

 cannot be rendered more so canribt be sub- 



