ON OUR rHESENT KNOWLEDGE OF THE CRUSTACEA. 239 



a nitrogenous body analogous in some respects to ui'ic acid, but less 

 highly oxidated ; if this be the case, there can be little doubt that the 

 green glaud rej^resents the kidnej-, and its secretion the urinary fluid, 

 while the sac is a sort of urinary bladder.' 



The evidence on which this newly-proposed use of the green gland 

 rests is the mild statement of Will and Gorup-Besanez (I quote from the 

 notes in Professor Huxley's 'Crayfish' '), who say that in this organ and 

 in the organ of Bojanus of the fresh-water mussel, they found ' a sub- 

 stance, the reactions of which, with the greatest probability, indicate 

 guanin,' but that they had been unable to obtain sufficient material to 

 give decisive results. 



"When we consider the position of this organ in its relation to the 

 other parts, as they ai'e arranged in separate genera, very definite analyses 

 ought to be determined before a cautious anatomist can accept this idea 

 as proven. 



There is an osseous tubercle on the first joint of the antenna that is 

 hollow, the orifice being covered by a thin translucent membrane, in the 

 centre of which there is a narrow pei-foration. This tubercle Milne-Edwards 

 and most carcinological students have thought to be the passage con- 

 nected with acoustic properties, but which I have always contended was 

 related to the olfactory sense ; but as the observations of Will and 

 Gorup-Besanez, although published in 1848, have been supported by 

 Wassiliew in 1878, and Huxlej' in 1879, it will be desirable to allude to this 

 tubercle by a name that will not commit its relation to any decided use 

 until so determined. I shall consequently write of it as the Fhymacerite? 



This organ is always in connexion with the coxa or first joint of the 

 second pair of antennfe, even in those Crustacea in which the antennaj are so 

 fused into the frontal region (or metopus), that without previous know- 

 ledge it is impossible to determine its relation to the antennfe. In these 

 cases, as in most of the higher types of the Brachyura, it is so concentrated 

 into the animal that it is very generally covered and protected by the 

 appendages of the mouth, and it is always closely associated with that 

 organ. Moreover, the watery sac is so delicate in its structure that it is 

 diflacult to dissect it without rupturing its walls — a circumstance that I 

 have never succeeded in doing in the Brachyura — and the passage of an 

 inserted bristle must puncture its walls at any point. 



In the Amphipoda the entrance is through a long spine, and the 

 membranous passage is slightly winding. In the Isopoda I never observed 

 any, at least conspicuous, tubercle. In the Brachyura it is generally closed 

 by an osseous ojjcrculum. 



Writing on this same organ, Milne-Edwards says : ' The Crustacea, or 

 at least those of the higher ordei's, possess also the sense of hearing ; the 

 experiments of Minasi, as shown by a number of daily observations, 

 furnish proof that, among a great number of these animals, there exists an 

 apparatus that appears to be the seat of this faculty. 



' This organ is situated on the inferior surface of the head, in advance 

 of the mouth, and behind the second pair of antennas, or even in the 

 basilaire joint of the antennae itself. In the crayfish, as exliibited by the 

 researches of Scarpa, it exists at this place on each side of the body — a 

 little osseous tubercle (Phymacerlie) of which the summit presents a 

 circular orifice which is closed by a thin, firm, and elastic membrane, 



' Gelehrte Anzei/jer d. li. Baienschen Aliademie, No. 233, 1848. 

 * <E>£jua, tubercle ; /ce'pos, horn (antennal tubercle). 



