Mr. T. H. Huxley on the Auditory Oryans in the Crustacea. 305 



sac in the first pair of antennae is the auditory organ, in the 

 second the olfactory organ. 



Although the structure of the organ contained in the first pair 

 of antennae in the Maa'oura departs somewhat from the ordinary 

 construction of an acoustic apparatus in the Invertebrata^ yet the 

 argument from structure to function, as enunciated in the paper 

 referred to, seems almost irresistible. Still, as it has obviously 

 not produced general conviction, I hope that the following evi- 

 dence may be considered as finally conclusive. 



In a small transparent Crustacean (taken in the South Pacific) 

 of the genus Palamon (fig. 2 a), the basal joint of the first pair of 

 antennae is thick, and provided with a partially detached ciliated 

 spine at the outer part of its base (fig. 3 a). Between this and 

 the body of the joint there is a narrow fissure. The fissure leads 

 into a pyriform cavity (fig. 3 b), contained within a membranous 

 sac, which lies within the substance of the joint. The anterior 

 extremity of the sac is enveloped in a mass of pigment-granules 

 (c) : on that side of the sac which is opposite to the fissure, a 

 series of hairs with bulbous bases are attached along a curved 

 line {d) ; these are in contact with, and appear to support, a large 

 ovoidal strongly refracting otolithe (e). 



The antennal nerve (/) passes internal to, and below the sac, 

 and gives off branches which terminate at the curved line of the 

 bases of the hairs. 



The sac is about y^gth of an inch in length ; the otolithe about 

 jl^^th in diameter. 



This structure is obviously very similar to the ordinary form 

 of auditory apparatus in the MoUusca, &c. In Lucifer typus 

 however we have an absolute identity. 



In this singular crustacean (PI. XIV. fig. 1) the basal joint of the 

 first or internal pair of antennae is much longer than the others, 

 and is slightly enlarged at its base. The enlargement contains a 

 clear vesicle (e), slightly enlarged anteriorly, but not communica- 

 ting by any fissure with the exterior. It is about ^^^th of an inch 

 in diameter. It contains a spherical strongly refracting otolithe 

 about -j-g Vo*^ *^f ^'^ m(i}(i in diameter, which does not present any 

 vibrating or rotating motion. We have here then Lucifer pre- 

 senting an organ precisely similar to the auditory sacs of the 

 Mollusca, while PaMmon offers a very interesting transition be- 

 tween this and the ordinary crustacean form of acoustic organ as 

 described by Farre, and there can I think be very little doubt 

 that the determination of the latter (as regards the Macroura at 

 least) was perfectly correct. 



. Since writing the above I find that the auditory organ in ha- 

 cifer has been recognised by M. Souleyet. All that he says about 

 Ann. if Mag. N. Hist. Ser. 2. Vol. vii. 20 



