PREFACE. 



THE STUDENT who would acquire a satisfactory 

 knowledge of the principles of Zoology is recom- 

 mended to commence by learning the elementary 

 principles of General Biology ; and having mastered 

 these he should then study the groups of the Inverte- 

 brates as here detailed, coupling his study with a 

 practical examination of such common types as are 

 easily to be obtained. A jellyfish, or a hydra, an 

 earthworm, an oyster, a snail, a cockroach and a 

 lobster, are forms everywhere procurable, and, if 

 examined, will give the student a good general idea 

 of the structure of Invertebrate Animals. It must be 

 borne in mind that without some such practical study, 

 no amount of reading will suffice to convey accurate 

 and adequate ideas of animal organisation. 



ALEXANDER MACALISTER. 



