ON OUH PRESENT KNOWLEDGE OF THE CRUSTACEA. 39 



the apparatus attached to the base of the first pair of antenna 1 , which, with 

 the exception of Rosenthal, appears to have been overlooked by most car- 

 cinological anatomists. Prof. Huxley, in the paper quoted, admits its 

 presence only in Macrurous Crustacea ; for he says, "It is universally ac- 

 knowledged that in the Macrura there exists in the basal joint, of both the 

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

 Brachyura such a sac exists, at least in the second pair." 



•• Although," the same author continues, " the structure of the organ 

 contained in the first pair of antenna? in the Macrura 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 (Dr. Farre's), seems almost irresistible. Still, as it has obviously 

 not produced general conviction, I hope that the following evidence may be 

 considered as finally conclusive." 



Mr. Huxley then describes and figures a small transparent Crustacean 

 (taken in the South Pacific) of the genus Palcemon; and states that the "basal 

 joint of the first pah.' of antenna? is thick, and provided with a partially 

 detached ciliated spine at the outer part of its base. Between this and the 

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

 cavity 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 ; on that side of the sac which is opposite to the fissure, a 

 scries of hairs with bulbous bases are attached along a curved line ; these are 

 in contact with, and appear to support, a large ovoid, strongly refracting 

 otolithe. 



" The antennal nerve passes internal to and below the sac, and gives off 

 branches which terminate at tho curved line of the bases of the hairs. The 

 sac is about T -> ro of an inch in length, the otolithe about vrL, T in diameter. The 

 structure is obviously very similar to the ordinary apparatus in Mollusca &c."' 

 A similar kind of formation I have observed in a species of Anchistia from 

 Australia ; and also Dana has figured a similar structure in the same 

 appendage of an Anchistia. It may be that Huxley's Palcemon may be a 

 species of Dana's Anchistia. 



The form of the otolithe observed by myself was irregularly ovoid. It is 

 described in the ' Proceedings of the Zoological Society ' for the 24th of 

 November, J 813, p. 5, pi. xxi. fig. 5G, where I observe that it " bears a near 

 resemblance to that which Van Rencden considers to be an otolithe, and 

 which was found by him in the inner ramus of the posterior pair of pleopoda 

 in some species of Stomapoda." 



Huxley likewise has observed and figured the same structure as being 

 present in the genus Lucifer ; where he says that " wo have an organ pre- 

 cisely similar to the auditory sacs of the Mollusca, while Palcemon offers a 

 very interesting transition between this and the ordinary Crustacean form of 

 acoustic organ as described by Farre." 



M. Souleyet has also noticed the structure in Lucifer, but only gives it a 

 passing notice, in Froriep's 'Notizen,' 1843, p. 83. 



The second and third joints appear to possess no peculiarity of structure, 

 but generally diminish in length and breadth, perhaps in a corresponding 

 ratio to the increased functional development of the first or coxal joint. 



A filaincntal appendage is almost universally attached to the extremity. 

 In some genera the lash is consolidated to a plate, as in Scyllarus, Ibaccits, 

 or rigid rod, as in Clydonia &o. ; but, as a rule, throughout the entire list of 



