378 Linnean Society. [April 17, 



decrease in a relative degree to the rest of the carapace. This, 

 •which is apparent in Macroura, is carried to the greatest extent in 

 the Diastylida, where the carapace is almost wholly constructed of 

 the mandibular ring, leaving but a small area in the centre as re- 

 presentative of the antennal rings. 



Lower in the scale we find that the same law still prevails, and 

 the author identifies the first ring in the Amphipoda with the man- 

 dibular ring in the Podophthalma ; the anterior three rings being 

 so diminished in importance and absorbed within the fourth, that 

 they are recognized by their appendages only. 



Secondly, the object of the author was to show, in this portion of 

 his paper, the functions with which each antenna is separately 

 endowed ; this was done by a relative comparison of the external 

 character of each with its internal structure. 



On removing one of the superior antennae from its position, and 

 examining the basal articulation, which is largely developed in the 

 whole of the Brachyura, the author found that the chamber formed 

 by the integumentary walls was occupied by a still smaller chamber 

 or cell, having calcareous walls of a more delicate character ; this 

 internal chamber bears a strong similitude to a true but low kind of 

 cochlea, which the author believed it to represent. 



This supposed cochlea is attached to the walls of the cavity 

 farthest from the median line of the Crab. It presents a tendency 

 to a spiral form, but passes not beyond a single turn ; it is supplied 

 by the third pair of nerves from the cephalic ganglion. 



In consequence of the presence of this internal cell in the base of 

 the internal antennae of the Brachyura, together with the constant 

 presence of fine membranous cilia upon the prolonged filament, the 

 author associates the sense analogous to hearing with these antennae 

 rather than with the external, to which it has been attributed by Dr. 

 Farre and Prof. Milne-Edwards, and which the present state of 

 science admits. But the author feels assured, from a careful exami- 

 nation of the external antenna, that it is not adapted for the purpose 

 of conveying sound. The organ of hearing is always so placed that 

 it may catch the first sound of approaching danger ; but the organ 

 in the lower antenna, described by Dr. Farre from the Macroura, is 

 in the Brachyura protected by a calcareous operculum, and is more- 

 over covered by the supplying organs of the mouth — two circum- 

 stances which destroy its efficiency as an organ of hearing ; whereas 

 its close proximity to the mouth may, by testing the character of 

 the passing material before taken as food, render its position 

 valuable for an organ of smell, which sense the author has been led 



