26 
THE VOYAGE OF H.M.S. CHALLENGER. 
believes lie lias observed segmental organs in each of the seven body segments. Whether 
M. Hnet be right in considering these organs “organes glandulaires . . . qui s’ouvrent a 
la partie superieure des epimeres, de chaque cote, par une ouverture en crible ” as segmental 
organs, I will not discuss. To judge from his description they have not the typical 
structure of true segmental organs which are to form an open communication between the 
body- cavity and the exterior. 
Two other sets of glands of Arthropoda, and more especially of Crustaceans, are 
perhaps more nearly related to the segmental organs ; they are the antennal glands of 
the larvae of many Entomostracans and of the full-grown Malacostracans ; and the shell- 
glands of full-grown Copepoda and Phyllopoda. According to Grobben 1 they have 
nearly the same structure, and must be regarded as homologous organs (homodynamous 
they are called, more accurately I think, by R. and 0. Hertwig 2 ) ; both are com- 
posed of a little terminal sack (Endsackchen), and a channel (Harnkanalchen) which 
opens at the surface of the body. Moreover, the cells covering the interior of the little 
sack in the antennal and shell-glands show a complete resemblance. An open communi- 
cation with the body-cavity has, however, never been observed in the case of these 
organs 3 ; if they really are to be compared with segmental organs, there can be no 
question that they have degenerated from their original condition. 
Should there ever be discovered an intermediate form between a true segmental organ 
such as that of Scalpellum and a shell-gland as observed in the Copepoda, then in the 
first place the homology of the apparatus may be accepted ; but in the second place it 
will then also be possible to give a more solid basis for demonstrating the homologies of 
the extremities of Cirripedia and Copepoda than has been the case hitherto. When treat- 
ing of the female genital apparatus and its orifice at the base of the first cirrus I hope to 
point out that there is sufficient reason for admitting that a second pair of segmental 
organs, though in a slightly modified condition, is present in the Cirripedia also. 
Finally, I will not take leave of this subject without stating as my opinion that the 
segmental organ which I have described is physiologically an organ of an excretory 
nature. The condition of the material at my disposal did not allow of my attempting a 
chemical investigation of the contents of the cells, and so it is only from analogy that 
this conclusion has been arrived at. It is fairly supported, I think, by the presence of 
muscle-fibres with numerous cavities between them, such as have also been observed 
by Grobben ( loc . cit., p. 105) in the neighbourhood of the antennal glands of the 
Decapoda. 
1 C. Grobben, Die Antennendriise der Crustaceen, Arh. Zool. Inst. Wien., Bd. iii. 1880. 
2 R. and 0. Hertwig, Die Coelomtlieorie, Jenaische Zeitschr., Bd. xv. pp. 1-150, 1882. 
3 According to Sedgwick {Quart. Journ. Micr. Sci., vol. xxiv., N.S., pp. 46, 47, 1884), the nephridia of the Inverte- 
brata are developed from solid masses of cells derived from the wall of the coelom ; a communication with the body- 
cavity in that case would represent a secondary stage. 
