NOTES AND OBSERVATIONS ON BOARD H.M.S. RATTLESNAKE 8 1 



Invertebrata for 1843-44,'^ mentions Dr. Farre's views, but seems to 

 doubt their correctness ; and they have had no better reception from 

 Prof Van der Hoeven ^ and Erichson.^ 



The matter stands thus at present then. It is universally acknow- 

 ledged that in the Macroura there exists in the basal joint of both the 

 first and second pair of antennae a sac containing a liquid, and that in 

 the Brachyitra such a sac exists at least in the second pair. According 

 to the majority of authors the sac in the second pair is the auditory 

 organ ; and according to Rosenthal the sac in the first pair is the 

 olfactory organ. 



On the other hand, if we take Dr. Farre's interpretation, the 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 Macroura departs somewhat from the ordinary con- 

 struction 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 evidence may 

 be considei'ed as finally conclusive. 



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

 the genus Palcemon (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 «). 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 id') ; these are in contact with, 

 and appear to support, a large ovoidal strongly refracting otolithe ie). . 



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 x^irth of an inch in length ; the otolithe about 

 -2-i-„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 (PL XIV. [Plate 10] fig. i) the basal joint 



^ MUUer's Archiv, 1845. ^ Handbuch d. Zoologie, p. 597. 



* Erichson's Avchiv, 1844. 

 VOL. I G 



