Until recently no definite excretory organs had been recognised, and the function of excreting the nitrogenous matter was by some assigned to the lemnisci. In 1893 Kaiser[217] described in _G. gigas_ two organs which he called nephridia, placed dorsally to the ducts of the male and female reproductive organs. Each nephridium, which somewhat resembles a cauliflower, consists of a stalk or duct, opening at one end into the reproductive ducts, and at the other branching and breaking up into a number of secondary and tertiary twigs. The end of each twig is closed by a membrane pierced with a number of most minute pores, by means of which it communicates with the body-cavity; on the inner side the membrane bears a number of long cilia, which keep up an active flickering. The presence of these cilia is interesting, as elsewhere they are unknown throughout the Nemathelminthes. [Illustration: FIG. 95.—A, A longitudinal section through the terminal twigs of the nephridium of _Gigantorhynchus gigas_. (From J. E. Kaiser.) Highly magnified. _a_, Nucleus. B, A terminal twig more highly magnified; _b_, the porous membrane.] The nervous system consists of a central ganglion situated in the proboscis sheath; it is oval and flattened in shape. The ganglion gives off nerves to the proboscis, and two main trunks which pierce the proboscis-sheath and run backward surrounded by a cluster of muscle-fibres, the whole being termed the {178}_retinaculum_; in the male they are in connexion with a special genital ganglion which lies near the ductus ejaculatorius. With the exception of certain sensory papillae in the neighbourhood of the male genital orifice, and of three similar papillae mentioned by Kaiser on the proboscis, the Acanthocephala are devoid of sense organs. The Acanthocephala are dioecious; their generative organs are developed in connexion with the _ligament_, a cord-like structure which arises between the inner and outer layer of the hinder end of the proboscis sheath and traverses the body-cavity, ending posteriorly in connexion with the genital ducts. The testes lie in this ligament; they are paired oval bodies which open each into a vas deferens. The vasa deferentia each bear three lateral diverticula, the vesiculae seminales; and three pairs of cement glands pour their secretion into a duct which opens into the vasa deferentia; the latter unite and open by a penis which is withdrawn into a genital bursa, but is capable of being extruded. [Illustration: FIG. 96.—An optical section through a male _Neorhynchus clavaeceps_ Zed. (From Hamann.) _a_, Proboscis; _b_, proboscis sheath; _c_, retractor of the proboscis; _d_, cerebral ganglion; _f_, _f_, retractors of the proboscis sheath; _g_, _g_, lemnisci, each with two giant nuclei; _h_, space in sub-cuticular layer of the skin; _l_, ligament; _m_, _m_, testes; _o_, glands on vas deferens; _p_, giant nucleus in skin; _q_, opening of vas deferens.]