xxviii THE VOYAGE OF H.M.S. CHALLENGER. 



urinary canal lie considers as a long convoluted tube, which opens on the calcified pro- 

 jection or phymacerite. 



Professor Huxley says in his work on the Crayfish 1 that — "The existence of guanin 

 in the oreen gland rests on the authority of Will and Gorup-Besaniz, 2 who say that in 

 this oro-an 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." 



In a memoir read before the Royal Society, Dr. A. B. Griffiths gave an account of his 

 chemical researches on the green glands of Astacus fluviatilis, in which he states that it is 

 a true urinary organ, and that its secretion contains uric acid and very small traces of 

 the base of guanin. 3 



More recently Herr Rawitz has given an account of his researches on the green gland 

 of the Crayfish 4 (Astacus fluviatilis). After giving an account of the researches of 

 Leydig, Wassiliew, Grobben, and others, he describes the gland, which, like Huxley, 

 he compares in shape to the fruit of the mallow, as consisting of three different substances, 

 oreen, white, and yellowish-brown. The green structure appears to be the outer shell or 

 skin, within which the two others are enclosed. It consists of homogeneous cells, with 

 a delicate contour, containing a well-defined nucleus, and a few clear green pigment 

 granules which have a tendency to collect and escape at one pole. The white substance 

 is characterised by the absence of all pigment and by the shining appearance of the 

 epithelium. The yellowish-brown substance owes its colour, not as Grobben says, to a 

 disposition of irregular bodies of a yellowish-brown colour in the protoplasm, but to the 

 presence of more or less intensely straw-coloured nuclei. 



The products of secretion found in the white portion are round dull globules with a 

 sharp contour hue and of a transparent homogeneous appearance. 



From a study of the general structure Herr Rawitz has arrived at the conclusion that 

 the green gland consists not of a single much-coiled tube, but of two which unite just 

 before the entrance to the sac ; of these the longer tube forms the green and the mass of 

 the white substance, while the second forms the yellowish-brown substance and a small 

 portion of the white. There is never any direct communication between the green and 

 the yellowish-brown substances. As to function, the author thinks that as yet, in the 

 absence of a more complete physiological investigation, it is premature to conclude that 

 the antennal gland of the Crayfish possesses the functions of a kidney. 



On the outer side of this joint in Palinurus an involuted fold exists in the hard wall 

 so as to form a fulcrum on which a process of the second joint rotates. Generally there 



1 P. 353. * Gelehrte Anzcigen d. k. Baierischen Akademie, No. 233, 1848. 



3 Proc. Roy. Soc, pi. xxxviii. p. 187, 1885. 



4 Archivf. mikrosk. A not,, Bd. xxix. p. 471, Taf. xxviii., xxix., 1887. 



