4826 Notices of New Books. 



animal be at rest, let it be feeding, no 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 disappear; and in Ligia and the amphibious 

 Orchestidae 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 oper- 

 culum 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 ob- 

 served, 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 membranous 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 suspended. 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 





