74 
Proceedings of the Royal Society of Edinburgh. [Sess. 
antero-posterior direction, and their dactylopodites catching into the ground 
resist a forward pull. Roughly, it may be said that the terminal claws, 
arranged along the border of the animal “ from bow to stern,’’ like so many 
boat-hooks held out from the side of a boat, give the animal an exceedingly 
firm grip ; as may be seen by placing the creature on a sheet of sand-paper 
and subjecting it from any quarter to the draught of an electric fan. 
The animal is thus excellently adapted for clinging. How the limbs 
are operated in progression need not concern us at present, and we shall 
avoid needless complications by postponing consideration of gait, which 
involves, in addition, a complex movement at the coxo-basal and a more 
simple movement at the mero-carpal articulation. The essential thing 
at tliis stage is to have a clear realisation of the general arrangement of 
this series of limbs, the long and powerful basipodites flexing medially 
under the body, the dactylopodites clutching the ground all along the 
lateral border. 
Different Types of Limb-Taxis in the Peracarida. 
Ligian Limb-Taxis in other Isopods . — While the Ligian variety of 
limb-taxis, associated with great clinging power, is a peculiarly isopodan 
feature, it is not characteristic of all the sub-orders. Perhaps in some 
Asellota, and certainly in the Phreatoicidea, and in the atypical Flabellifera, 
different arrangements prevail. From the point of view of walking limbs, 
the purely parasitic Epicaridea may in the meantime be neglected. In the 
more typical Flabellifera, in many Valvifera, and in the Oniscoidea the 
limb-taxis is Ligian. Some points of general interest here arise. 
Members of the three last-named sub-orders resemble each other and 
differ from other Isopoda in the fact that the coxopodites of the walking 
limbs have become expanded into coxal plates more or less rigidly 
connected with the body. In the Asellota and in the Phreatoicidea the 
coxopodites are small and movable. One might be inclined to associate 
rigidity and lateral expansion of coxopodites with Ligian limb-taxis were 
it not that in some Asellota the taxis is like that in Ligia. 
The typical Flabellifera and the Valvifera use the thoracic limbs chiefly 
for clinging, not so much for progression. While one naturally correlates 
the parasitic habits of Flabellifera with this peculiarity, a potential 
capacity for a similar life, so far as limbs is concerned, may be seen even in 
vegetable-feeding Idoteae. One has only to place an Idotea haltica in a 
vessel containing sea-water and a small fish, say, a slippery gunnel, to 
realise this. Whatever the immediate object, whether clinging to animal 
prey or to seaweed, the thoracic limbs of these animals serve as hold-fasts 
