436 A HISTORY OF RECENT CRUSTACEA 
CHAPTER XXVIII 
CONCLUSION 
To complete the sketch of the Malacostraca, the sub-order 
of the Amphipoda remains to be described. These crusta- 
ceans may be defined in a very simple manner as Edrioph- 
thalma having branchial sacs or vesicles connected with 
some or all of the last six of the seven pairs of limbs 
normal to the perzeon or trunk. Of all the divisions of 
the sub-order which have been proposed, that which 
arranges them in three tribes, the Gammaridea, Caprel- 
lidea, and Hyperidea, still seems the most satisfactory. 
Chapters describing these tribes for this volume had been 
already written, when it appeared that they overflowed 
the utmost space that could be allowed. As room for 
them could only be found by an unsatisfactory curtailment 
of the earlier portions of the work, I have preferred to 
leave over this last section of the Malacostraca, hoping to 
engage the reader’s interest in it at no distant future. 
For the exclusion of a group so important as the 
Amphipoda, and one so obviously within the scope of the 
present pages, an apology is doubtless due, but little or 
none need be offered for the omission of much else which 
the student might desire to know, since the extent of the 
subject and the limits of the volume must make it clear 
that no other course was possible. It would take a 
volume by itself to analyse in an effective manner the long 
and valuable disquisitions which have been written on the 
circulation, the nervous system, the viscera, the tissues, 
the intimate structure of the various organs of the senses, 
the connection between fossil and recent forms, and the 
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