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 perason or trunk. Of all the divisions of 

 the sub-order which have been proposed, that which 

 arro.nges 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 



