26 NOTICES OF SERIALS. 



matter, the superior antenna is ever elevated, and on constant guard. Again, if 

 we turn our attention to the land Crustacea, we find the organ, as an antenna, dis- 

 appear ; and in Ligia and the amphibious Orchestidce they are rudimentary, as if 

 the organ, passing from water into a less dense medium, required modification in 

 order to adapt it to the change of circumstances. If we take into consideration the 

 nature of sound, and its difference of character when conveyed under water from 

 that of passing through air, the obtuse character of the former, which can scarcely 

 be more than a vibratory action of particles of water, which conveys to us a very 

 modified and imperfect idea of sound, we find it difficult to understand that the 

 organ situated at the base of the under antenna is capable of receiving impressions 

 of sound, enclosed as it is within and covered by a stout calcareous operculum. 

 But if we view it as an organ of smell, every objection previously becomes evidence 

 in favour of the idea. The small door, when it is raised, exposes the orifice in a 

 direction pointing to the mouth ; this, also, is the direction of the same organ in all 

 the higher orders. In Amphipoda it is directed inwards and forwards. In every 

 animal it is so situated that it is impossible for any food to be conveyed into the 

 mouth without passing under this organ, and of this the animal has the power to 

 judge its suitability for food by raising the operculum at will, and exposing to it 

 the hidden organ the olfactory. If we turn to the upper antenna, we find that its 

 position, form, and power, are as capable of fulfilling the office of conducting the 

 sensation of sound, as the lower is that of smell. As I before observed, it is always 

 placed erect, and continually feeling in the water for the first approximation of 

 sensation. The filamentary appendages are always two or more, one of which is 

 supplied with singularly- delicate membraneous cilia, being apparently prolongations 

 of a similar membrane to that which covers the larger orifice of the olfactory 

 organ. These lengthened and delicate cilia are peculiarly adapted to receive and 

 convey the most minute vibratory sensation of the medium in which they are sus- 

 pended. These organs, when spoken of, may conveniently be designated as auditory 

 cilia, and have been found in every species of Crustacea that has been searched for 

 them. If we turn our attention to the internal structure of this antenna, we shall 

 find that it supports the idea of its being an auditory organ more forcibly than its 

 external analysis. In the Brachyura, as before observed, the first, or basal 

 articulation is largely developed ; if it be removed from its connection 

 with the animal and broken open, the basal articulation will be found 

 occupied by a still smaller chamber, having calcareous walls of a much 

 more delicate character than the integumentary structure. This internal 

 chamber or cell is that which, in this paper, is supposed to be a cochlea, from 

 its analogy, both in its structure and supposed use, to that organ in higher animals. 

 It is situated in the cavity of the basal articulation of the antenna, and attached to 

 the walls furthest from the median line of the crab. It presents a tendency to a 

 spiral form, but passes not beyond the limits of a single convolution. The calca- 

 reous walls extend across the axis of the ideal spire, and the internal cavity is one 

 continuous irregular chamber, the walls of which, at the centre of the axis, closely 

 approximate, so as almost to meet. 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 



