The larvae (Fig. 99, A) are purely aquatic, and are highly modified for this life, being elongate creatures, with sharp, mandibles and nine abdominal segments, each segment bearing on each side a trachea branchia; these gills assist to some extent in locomotion. The stigmata are quite obsolete, but the terminal segment bears four processes, one pair of which may be looked on as cerci, the other as a pair of gills corresponding with the pair on each of the preceding segments. The mandibles are not suctorial, but, according to Meinert, possess an orifice for the discharge of the secretion of a mandibular gland. Gyrinidae are chiefly carnivorous in both the larval and imaginal instars. Fully 300 species are known; they are generally distributed, though wanting in most of the islands of the world except those of large size. The finest forms are the Brazilian _Enhydrus_ and the _Porrorhynchus_ of tropical Asia.[97] In Britain we have nine species, eight of _Gyrinus_, one of _Orectochilus_; the latter form is rarely seen, as it hides during the day, and performs its rapid gyrations at night. The Gyrinidae are one of the most distinct of all the families of Coleoptera: by some they are associated in the Adephagous series; but they have little or no affinity with the other members thereof. Without them the Adephaga form a natural series of evidently allied families, and we consider it a mistake to force the Gyrinidae therein because an objection is felt by many taxonomists to the maintenance of isolated families. Surely if there are in nature some families allied and others isolated, it is better for us to recognise the fact, though it makes our classifications look less neat and precise, and increases the difficulty of constructing "tables."