Definition of Crustacea. 
11 
Class i. — CRUSTACEA. 
INTRODUCTORY. 
The exhibited series of Crustacea occupies the southern part of 
the “ Insect Gallery.” The Table-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 their 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 
