Definition of Crustacea. 11 



Class i.-CRUSTACEA. 



INTEODUCTORY. 



The exhibited series of Crustacea occupies the southern part of 

 the "Insect Gallery." The Tal:)le-cases Nos. 1-16 contain a series 

 of typical representatives of the various Sub-classes and Orders 

 composing the Class, arranged in systematic order. The Wall- 

 Cases Nos. 1-6 contain exhibits illustrating the structure and 

 life-history of the Lobster, and forming an introduction to the study 

 of the Crustacea; a number of specimens illustrating the habits 

 and mode of life of various Crustacea; and sundry specimens 

 which, by reason of tlieir size, could not conveniently be exhibited 

 in their proper places in the systematic series. 



DEFINITION OF CRUSTACEA. 



The Class Crustacea, as understood by modern zoologists, 

 comprises the forms commonly known as Crabs, Lobsters, Cray- 

 fish, Prawns, Shrimps, Sandhoppers, Woodlice, Barnacles, and 

 Water-Fleas, besides a multitude of related forms undistinguished 

 by any popular names. It does not include the King-Crabs 

 (Xiphosura) and Sea-Spiders (Pycnogonida), formerly associated 

 with it, but now regarded as more closely related to the Arachnida. 



The Crustacea differ so widely among themselves that it is 

 very difficult to give a definition of the group which will apply to 

 all its members, and it is hardly possible to do so without entering 

 into highly technical details of structure and development which 

 would be out of place here. 



It may be said, however, that they differ from Insects, 

 Arachnida, and the other groups which, together with Crustacea, 

 form the comprehensive group (Phylum or Sub-Phylum) Arthro- 

 poda, in having two pairs of antennae (feelers) in front of the 



