VI PEE FACE 



of the creatures there is much to afford entertainment, 

 and almost every new observer finds something singular 

 to relate. 



In examining the structure both external and internal r 

 whether in new species or in those that have been long 

 established, the acutest powers of observation may be 

 trained and profitably employed. Moreover, the highest 

 ingenuity is excited and finds scope in the effort to explain 

 the meaning of the facts observed. For, judging by dis- 

 coveries already made, we are warranted in supposing 

 that, down to the finest hair, every detail of every organism 

 has its motive and meaning. Nor need man despair of 

 finding out something for his private and personal benefit 

 while investigating the physiology of a shrimp. 



It is needless to insist that a hundred volumes such as 

 the present would not suffice to discuss the subject in all 

 its bearings, since a hundred volumes would be but a 

 small fraction of what has been already written upon it, 

 and the incessant stream of publications widens and 

 deepens as it flows. 



By the references made to some of the most recent 

 and to some of the most important authorities, the student 

 will be guided in general to adequate lists of literature. 

 In consulting these bibliographical notices he will be 

 perhaps as much amazed by the multitude of writers and 

 writings as at first by the multitude of the genera and 

 species of the Crustacea themselves. He will be led to 

 consider it not unreasonable that the present volume 

 should have been content to deal with one half of the 

 entire class, leaving the other half for a future occasion. 



