162 Proceedings of the Royal Physical Society. 



tuft of tactile setse at the base of the procerite, and a few are 

 continued from that point down the outer margin of the 

 carpocerite ; but all the setse below that point on the upper 

 surface are fringing setse, as that part is covered by the 

 antennules and the squame. On the squame there are only 

 fringing set«, very long and strong, arranged in a single row 

 along its inner margin, and which evidently serve merely to 

 increase the surface. On the under surface of the basal 

 segments of the antenna there are no setse. 



Experimental. — According to Lemoine, the point of the 

 antenna is very sensitive ; this I am able to confirm. The 

 rest of the procerite is sensitive, but not nearly so sensitive 

 as the antennules. It seems strange, at first sight, that the 

 setee on the " feeler," as it is so often called, should be small, 

 — and I may remark, in passing, that on the antennae of the 

 lobster they are still smaller, — but when we consider the 

 amount of rough usage which the antennae have to go 

 through, it is evident that, if the setae were longer and the 

 proportion of breadth to length therefore less, they would be 

 more fragile and in constant danger of mutilation. 



MancliUes. — On the great coxopodite there are only a few 

 short tactile setae on the posterior margin, and a few fringing 

 setae on the ventral surface. On the palp, all the setae on 

 inner side, which is applied closely to the corpus mandibuli, 

 are fringing setae, and the seta3 on the outer side of the first 

 joint of the palp are of the same nature. There are a few 

 scattered tactile setae along the outer and anterior margin of 

 the second joint, but the outer (i.e., anterior) edge and tip of 

 the third joint are covered with setse, the great majority of 

 which are certainly tactile; but as the setae are generally 

 covered with growths of various kinds, and the palp is very 

 opaque, I could not decide whether all were tactile. The 

 tactile setae here are peculiar, in that they are almost always 

 slightly serrated in their distal portion, and are short and 

 stout, with a narrow lumen. 



Maxillm. — The arrangements of the tactile setae on the 1st 

 and 2d maxillae is practically the same ; in both there are 

 several rows along the inner margin of the lacinias interna 

 and externa. In the 1st maxilla the setae are shorter and 



