PREFACE. IX 



mitted to culture, and propagated more exten- 

 sively by artificial means, and thereby increase 

 the benefits we derive from it. 



To exhibit the actual state of this inte- 

 resting question is the task I have imposed 

 upon myself in the present work, which em- 

 braces the practical history of a great number 

 of animals, and from which I find it impos- 

 sible to exclude even the microscopic In- 

 fusoria. 



When opportunity has been afforded I 

 have mentioned a few peculiarities observable 

 in several species, for it has been my endea- 

 vour to render the following pages interest- 

 ing to the general student, as well as to the 

 practical zoologist. 



LONDON, January, 1864. 



