44, A HISTORY OF RECENT CRUSTACEA 
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. 
Jn 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, 138, 14. The appendages of the five follow- 
ing segments have been and may sometimes conveniently 
be called perzeopods, 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 perzeon, 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. 8. Packard, unaware of what was intended by 
