44 A HISTORY OF EECENT CEUSTACEA 



further be noticed tHat there are Crustacea in which one 

 or other of the joints, most often the fifth, is itself multi- 

 articulate, thus adding to the normal number, which on 

 the other hand is still more frequently diminished by 

 coalescence, absorption, or complete failure of develop- 

 ment, affecting various parts of the limb. 



9. The ninth segment carries a very important and, 

 at the same time, very variable pair of appendages, which, 

 as the third maxillipeds, have in the higher Crustacea the 

 same kind of opercular character that has been noticed as 

 pertaining to the appendages of the seventh segment in 

 some of the lower groups of the Malacostraca. In his 

 celebrated and valuable work on the Crustacea of Japan, 

 de Haan made great use of these third maxillipeds for 

 classifying the Malacostracan group in respect to families 

 and genera. The various joints of the endopod by their 

 shapes, relative size, number, and mode of articulation 

 one with another, have yielded a multitude of characters. 

 In the Amphipoda, where the appendages of the ninth 

 segment are not mouth-organs, but constitute the second 

 gnathopods, they are commonly the most powerful limbs 

 of the trunk, being, no doubt in general, the animal's most 

 efficient weapons for holding its prey. In the Isopoda, on 

 the other hand, they are to be called gnathopods only by 

 courtesy, being in general little distinguishable from the 

 following pair of limbs. 



10, 11, 12, 13, 14. The appendages of the five follow- 

 ing segments have been and may sometimes conveniently 

 be called peraeopods, which means walking-feet. Among 

 the Amphipods and Isopods they are usually adapted for 

 walking, and in those groups the trunk, to which they are 

 attached, is often called the perteon, intended to signify 

 the ambulatory part. Among the crabs and lobsters, and 

 various other crustaceans, however, the first of these pairs 

 is by no means adapted for walking, but ends in large 

 claws or nippers, on account of which they are known as 

 the chelipeds, and Mr. J. E. Ives proposes to call the four 

 following pairs cruripeds, which means leg-feet, while 

 Dr. A. S. Packard, unaware of what was intended by 



