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Proceedings of the Royal Society of Edinburgh. [Sess. 
reach perhaps of half * the body length, which arrangement in turn would 
imply that, if the animal remains horizontal, the anterior two pairs are 
employed well forwards.f 
The second pair has the greatest lateral stretch, and probably extends 
farthest on either side during walking, while the last pair moves in lines 
nearest to the central axis. If the animal walks horizontally, it probably 
carries its body at some considerable height above the walking-surface ; 
this is suggested by the direction and length of the basipodites, by the 
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V 
> 
f 
N 
t 
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Fig. 7. — Two diagrams to illustrate possible varieties of gait in 
a pair of limbs. 
The central vertical lino in each of the diagrams represents the axis of 
the body ; the two thinner lines on each side represent the excursion of the 
dactylopodites relative to some fixed point in the body axis The animal is 
supposed to be moving towards the top of the page, and the dactylopodites, 
represented by arrowheads, are in contact with the ground. A, simultaneous 
movement of limbs ; B, alternate movement. 
length of the dactylopodites, and by the fact that space must be allowed 
for the opening of the uropodal valves. On the other hand, it may move 
over the bottom with head depressed and pleon pointing upwards. 
It may be mentioned that the mode of operation of the limbs might 
well be of high comparative interest. We have here an animal whose 
walking limbs have been reduced from the normal complement of seven to 
four. Does the central nervous mechanism function in the same way as 
the corresponding mechanism of the last four walking limbs of Ligia, or 
has it developed different functional peculiarities ? Have all the limbs the 
same period ? Are they assisted by the pleopods, and is their action in any 
way centrally correlated with the motor mechanism of the pleon ? 
* This statement is based on examination of the gait of Ligia , whose limbs are employed 
with a reach of just half the body length. 
f Since this was written, Mr R. S. Clarke, who accompanied Sliackleton’s recent 
expedition, has informed me that Glyptonotus carries its anterior perseopods in front of the 
centre of gravity of the body, and that pairs of limbs are used alternately. 
