164 Proceedings of the Royal Physical Society. 



podite is the longest segment, and on it the setae are placed 

 ventrally (in the normal position of the animal) to the true 

 edge, which is formed by a row of sharp tubercles. From 

 the meropodite onwards the same modified fringing setse are 

 present, as on the 2d maxillipede,' but on the dactylopodite 

 the tactile setse are all long and slender. On the external 

 margin of the more distal segments are a few tactile 

 setffi arranged irregularly. On the ventral surface of the 

 appendage are a good many small groups of tactile setse, 

 and on the exopodite are a few setse scattered here and 

 there. 



Ex'perimental. — If the rows of setse on the ventral surface 

 and inner edge of the 3d maxillipede be touched, these 

 gnathites on both sides are at once brought together, and the 

 great claw and the ambulatory limbs are brought down to- 

 wards the ventral surface. The exopodites of the 2d and 3d 

 maxillipedes are also slightly sensitive. It is interesting to 

 notice that the 3d maxillipede, which covers in all the other 

 jaws and jaw-feet, is especially well furnished with tactile 

 setse, while on those appendages internal to it, merely the 

 road to the mouth is lined with tactile setse. 



Metastoma. — The single row of setse on the inner edge are 

 delicate fringing setse ; there are no tactile setse. 



Thoracic Sterna. — The posterior sterna, especially the 4th 

 and 5th, are sensitive, and on examination tufts of setae are 

 found, a certain number of which are tactile. 



4ith to 8th Thoracic A2Dpendages (great claw, 2 lesser claws, 

 and posterior walking legs). — These five appendages have 

 none but tactile setse in a functional state on that part of 

 the limb which acts as a walking leg or a prehensile organ. 

 The arrangement on the " hand " of the great claw has already 

 been described in a general way. On the opposed edges of 

 the propodite and dactylopodite, between the tubercles which 

 stud them, are groups of tactile setse (PL YIIL, Fig. 4 ; PL 

 IX., Fig. 17) from 15 or 20 to 30 or more in each group. 

 Each tuft is roughly circular, and the longest setse, as a rule, 

 are in the middle, so that the whole tuft forms a cone. The 

 bases of the setse are crowded close together, and the setse 

 themselves are thick, strong, and comparatively short, and 



