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Proceedings of the Royal Society of Edinburgh. [Sess. 
vertebrates is subserved by these organs. In connection with Glyptonotus 
one might draw special attention to the elaborate and beautifully regular 
arrangement of setae on the ventral aspect of the segments of the walking 
limbs other than the basipodites and dactylopodites. The animal would 
seem to afford exceptional opportunity for experiment on the function of 
these sense organs. 
The Gnathopods. 
Striking features of these limbs are : (1) the adjustment to move in 
parallel planes close to each other and the abrupt change in direction of 
the principal plane of movement compared with the mean direction of 
the principal planes of the perseopods ; (2) slenderness of the basipodites ; 
(3) shortness of the post-ischial axis, owing especially to reduction in 
length of the merum and carpus, which diminishes the lateral or antero- 
lateral reach of the limb ; (4) vertical depth of the propus and recurvature 
of the dactylus to form a grasping finger ; and (5) dense aggregation of 
setas along the ventral border of the mero-carpo-propus. In addition to 
this a ventrally projecting rim on the lateral aspect of each coxal foramen 
(see fig. 2) prevents such extreme extension of the basipodite as occurs in 
the case of the perseopods ; any two gnathopods of a pair can be opposed in 
the middle line, the permopods being incapable of medial apposition. We 
may take up these peculiarities, not severally, but conjointly. 
Prehensile limbs in all animals tend to develop in close association with 
the head, which carries the mouth and certain specialised sense organs. 
So true is this that when we find exceptions we look for the operation of 
special conditions. Thus, grasping power on the part of the hind limbs of 
vertebrates is found in the climbing Primates and among birds. Phronima 
sedentaria among amphipods, which has the fifth pair of thoracic limbs 
chelate, is exceptional in its place of abode. The occurrence of a group of 
three anterior pairs of grasping limbs, all similar, appears to be limited to 
the Glyptonotinse, and is a very special feature of their organisation. 
It may be that the natural food of these animals is at times difficult to 
handle, demanding the conjoint manipulation of many limbs. In the gut 
of two dissected specimens I found numbers of amphipods almost intact. 
It is not impossible that the brush of setse on the propus is in part an 
adaptation for securing these smooth-bodied creatures. Glyptonotus, how- 
ever, eats dead meat as well as amphipods, as is shown by the presence of 
mammalian or avian muscle and connective tissue among the gut contents 
— cf. p. 248. It also eats ophiuroids. 
All three gnathopods have a forward reach to a transverse line a little 
