2l6 COLEOPTERA CHAP. 



downwards but towards one another ; hence the sensitive ad- 

 hesive surface used during coupling is placed on the side of the 

 foot, forming thus a false sole : a remarkable modification other- 

 wise unknown in Insects. They breathe chiefly by means of the 

 very large metathoracic spiracles. 



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 tracheal 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 Enliydrus and 

 the Porrorhynchus of tropical Asia. 1 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 Aclephagous 

 series ; but they have little or no affinity with the other mem- 

 bers 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 tax- 

 ouomists 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 classifi- 

 cations look less neat and precise, and increases the difficulty of 

 constructing " tables." 



Fam. 12. Hydrophilidae.--T#m five-jointed, the first joint 

 in many cases so small as to be scarcely evident: antennae 

 short, of less than eleven joints, not filiform, but consisting of 



1 For classification and monograph of the family, see Regimbart, Ann. Svc. ent. 

 France, 1882, 1883, and 1886. For a catalogue, Severin, Ann. Soe. cnt. Hclyiqi" , 

 xxxiii. 1889. 



