and on the Function of the Antenna in Crustacea. 45 



This internal cell represents, we think, the cochlea of higher 

 animals, to which it bears some resemblance both in form and 

 structure. If so, then beyond dispute it identifies the superior 

 antenna as an organ of hearing. 



The internal structure of the inferior antenna differs very 

 materially from the appearances we have just described. In the 

 Brachyura, where the organs are most fully developed, there is 

 attached to the operculum a long osseous tendon or lever, by 

 which the attached muscles raise or close the entire organ, but 

 there is no internal structure of any kind which could identify 

 it as being an organ of sound. The aqueous sac mentioned by 

 Edwards I have entirely failed to discover. 



Viewing the two autennffi each as a whole, in their relative posi- 

 tions and connexion with the rest of the animal, we are forcibly 

 led to the conviction that the upper antenna is an organ of 

 hearing, and the lower antenna is an organ of smell. 



EXPLANATION OF PLATES L and IL 



Plate I. 



Fig. \. The ophthalmic ring and appendages of Cancer Pagurus isolated 



from its position. 

 Fig. 2. The internal aspect of the two antennal and the anterior portion 

 of the mandibular rings of Cancer Pagurus. 



F F F shows the hne of fractm-e in consequence of the removal of 

 the upper portion of the carapace. 



AAA. The inner or anterior antennal ring, the supposed limits of 

 which are shown in dotted lines. 



to. The fossa which is exposed by the removal of the ophthalmic 

 segment. 



X, X. The internal extremities of the orbits. 



y, y. Cavity exposed by the removal of internal antennae. 



B B B B. The external or posterior antennal ring, the limit of 

 which is defined anteriorly where it is fused with the anterior 

 antennal ring by the dotted Une, posteriorly by the margin of 

 the oesophageal opening IE, by a ridge between B and C, where 

 a line of separation is often, if not always visible, and the line P, 

 which splits in some of the Brachyura when they throw off the 

 exuviae. 



z. The white spot in the deep hollow shows the position of the 

 olfactorj- organ (auditorj- of M. Milne-Edwards, Von Siebold, 

 &c.). 



C C C C. The fourth or mandibular ring ; epimeral of Prof. Milne- 

 Edwards*. 



m, m. Calcareous tendon of mandible. 



* The author anticipates being able to demonstrate, in the Report on the 

 Amphipod Crustacea for the British Association, that the so-called epi- 

 merals of the thorax, in the Sessile-eyed Crustacea, are in fact the first joint 

 of the leg. If this be correct, and the so-called epiraerals in the Brachyura 

 be admitted as the fourth or mandibular ring, the side pieces or epimerals 

 of authors will be found to have no existence, — a circumstance which the 

 author affirms to be the case. 



