Excretory system.—The excretory organs consist of a (a) pair of so-called "shell glands," which are considered to be the equivalents of the excretory tubes or nephridia of annelid worms. In the woodlouse these excretory organs open on the second pair of maxillae. They are composed of a tube (sacculus) closed at one end and more or less bent upon itself (5, p. 261) which communicates with a labyrinth that is provided with an excretory orifice. Matters are eliminated by the epithelial cells [the histology has been described and figured in Ligidium hypnorum (66)], which are very large in Ligia oceanica.
(b) Masses of cellules in the head, very greatly developed in Ligia oceanica (but numbering scarcely more than ten in Oniscus asellus), which have no external opening. They also function as excretory organs (5, p. 263), and have been called "cephalic nephrocytes."
(c) Other "branchial nephrocytes" are situated on the dorsal surface between the last thoracic and the first abdominal segments, as well as between those that follow, with the exception of the last two; they are in distinct patches, one on each of the middle line in Ligia, but more or less continuous in Oniscus (5, p. 265).
(d) The digestive glands have also been shown to be excretory (5, p. 270).
Nervous system.—The nervous system consists of paired ganglia in the head, above the alimentary canal which send off nerves (commissures) that meet below, to form a double nerve cord with ganglia at intervals (see fig. 19).
Reproductive organs.—In the female there are a pair of ovaries in the positions shewn in fig. 20; and ducts run to the underside of the fifth thoracic segment.