assuming an hydropic appearance. The growth itself seems to continue in most fishes for a great length of time, and we can scarcely set bounds to--certainly we know not with precision--the utmost range of the specific size of fishes. Even among species in no way remarkable for their dimensions we sometimes meet with old individuals, favourably situated, which more or less exceed the ordinary weight and measurement of their kind. However, there are certain evidently short-lived species of fishes which attain a remarkably uniform size within a very short time; for instance, the Stickleback, many species of _Gobius_ and _Clupea_. * * * * * The organs of nutrition, manducation, and deglutition, are lodged in two large cavities--an anterior (the mouth or _buccal cavity_), and a posterior (the _abdominal cavity_). In the former the alimentary organs are associated with those fulfilling the respiratory functions, the transmission of food to the stomach and of water to the gills being performed by similar acts of deglutition. The abdominal cavity commences immediately behind the head, so, however, that an extremely short thoracic cavity for the heart is partitioned off in front. Beside the alimentary organs it contains also those of the urogenital system and the air-bladder. The abdominal cavity is generally situated in the trunk only, but in numerous fishes it extends into the tail, being continued for some distance along each side of the hæmal apophyses. In numerous fishes the abdominal cavity opens outwards by one or two openings. A single _porus abdominalis_ in front of the vent is found in _Lepidosiren_ and some Sturgeons; a paired one, one on each side of the vent, in _Ceratodus_, some species of Sturgeon, _Lepidosteus_, _Polypterus_, _Amia_, and all Chondropterygians. As in these fishes semen and ova are discharged by proper ducts, the abdominal openings may serve for the expulsion of semen, and those ova only which, having lost their way to the abdominal aperture of the oviduct, would be retained in the abdominal cavity. In those _Teleosteans_ which lack an oviduct a single _porus genitalis_ opens _behind_ the vent. The _mouth_ of fishes shows extreme variation with regard to form, extent, and position. Generally opening in front, it may be turned upwards, or may lie at the lower side of the snout, as in most Chondropterygians, Sturgeons, and some Teleosteans. Vogt regards this position as a persistent fœtal condition. In most fishes the jaws are covered by the skin, which, before passing over the jaws, is often folded, forming more or less fleshy lips. In the Sharks the skin retains its external character even within the teeth, but in other fishes it changes into a mucous membrane. A _tongue_ may exist as a more or less free and short projection, formed by the glosso*-hyal and a soft covering, or may be entirely absent. _Salivary_ glands and a _velum palati_ are absent in fishes.