=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_. [Illustration: Fig. 17.--THE ALIMENTARY CANAL. (_Oniscus asellus._)] [Illustration: Fig. 18.--THE CIRCULATORY SYSTEM. (_Oniscus asellus._)] (_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." [Illustration: FIG. 19.--THE NERVOUS SYSTEM. (_Oniscus asellus._)] (_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). [Illustration: FIG. 20.--FEMALE REPRODUCTORY ORGANS. (_Oniscus asellus._)] =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. The openings are very difficult to identify, and Lereboullet (39, p. 113) was unable to find them. It is obvious that the openings must be underneath the plates that form the egg pouch, and as a change of skin is required to set these free, it would appear that at ordinary seasons the ducts from the ovaries are closed. The writers have been able to determine from external examination of specimens which had moulted and were about to lay eggs, that the oviducts at such time open to the inside of the base of each walking leg on the fifth segment. In similar specimens the oviducts were also followed to the opening from within. The _brood pouch_ has already been described. The male organs consist of six _testes_ arranged in two pairs, each of which is provided with a _reservoir_ (see fig. 21). The efferent ducts from the two reservoirs unite at the base of the thorax to form a common duct (or "penis"). [Illustration: FIG. 21.--THE MALE REPRODUCTORY ORGANS. (_Oniscus asellus._)]