94 ' THE REPOET OF THE I^^o. 36 



agent by which air is transferred to the pile covering the under surface of the 

 body. It is extremely interesting to watch a hydrophilid beetle come to the 

 surface, break the surface film by means of its antennae and bending it back so 

 as to touch the prothorax there is formed an opening bordered by the angle 

 between the head and pronotum and the antennae outside. Down this opening 

 the transfer of air takes place. How it is done I do not know. So far I have 

 discussed ©nly the adult Coleoptera. All larvae of Dytiscidae obtain their air 

 supply by coming to the surface, the terminal segment of the body usually being 

 provided with a large pair of spiracles. This is also the case with most Hydro- 

 philidae, though a few undoubtedly obtain their air supply by means of tracheal 

 gills (Berosus). In the Haliplidae I have described the method of securing an 

 air supply by the larvae of Peltodytes. This method is probably one of the most 

 remarkable yet described for Coleoptera. In the Donaciinae the larvae live on the 

 submerged roots and stems of aquatic plants, spatterdock, etc., and obtain their air 

 supply by puncturing the stem by means of two powerful anal spines. At the base 

 »f these spines are 'the spiracles which are thus placed in contact with the air in 

 the inter-cellular spaces of the plant. This is certainly one of the most remark- 

 able adaptations for the obtaining of an air supply. 



In the Diptera there, are many aquatic larvae which obtain their air supply 

 directly at the surface of the water. This is found in the aquatic Crane-flies, the 

 soldier flies, Culicidae and others. In the Syrphidae we find the rat-tailed maggot 

 which is provided with a long anal process. This is projected through the surface 

 film while the possessor revels in the filth below. 



There are three ways by which aquatic larvae may obtain their air supply 

 from that dissolved in the water. 



(1) Extremely thin-skinned forms which live among algae or rushing water 

 where oxygen is abundant. Here we have Ceratopogon (Punkies) in algae, some 

 very small non-case building caddis worms and a few stone flies (Chloroperla) 

 wliich live in rapids. 



(2) Blood gills. This, the true mode of respiration among aquatic organ- 

 isms, is rare in the insect group. We find it practically confined to a few 

 dipterous forms as Chironomus, Simulium, and an amphibious Cranefly, etc. 



(3) Tracheal gills. This method of securing an air supply is widely dis- 

 tributed and is but a modification of the ordinary tracheal respiration. Tracheal 

 gills are only extensions of the body wall into which run tracheae and their 

 attendant tracheoles. These are found «nder several different forms : — 



(1) Filamentous as in the Caddis-worms, Stone-flies, some Lepidoptera 

 (Paraponjx), and is probably the most primitive. 



(2) Lamelliform as in many Mayfly nymphs, and Damsel-flies. 



i r (3) Modification of the posterior end of the alimentary canal, Dragonflies. 



I shall not attempt to discuss at any length man^ of the other modifications 

 necessary for aquatic life. As the aquatic Coleoptera have become better fitted 

 foD rapid locomotion than any other forms it may be well to glance at their 

 adaptive modiications. Prof. Osborn in the American N"at. for Oct., 1903, has 

 described and adaptive modifications of aquatic mammals. Pro'f. Needham and 

 Miss Williamson in the same magazine for Aug., 1907, have shown that many of 

 these modifications find their parallel in the Oytiscidae. I may mention some 

 of them; (1) Eigidity of the body which has been brought about by compacting 

 and co-adaptation of the external parts of the skelton. This co-adaptation has 



