WATER-BEETLES. 



Fi^.24. 



LARVA. 



The water-beetle (Dytiscus) is represented in the larva state 

 (fig. 24), in the nympha state (fig. 25), in the imago or perfect 

 insect (jig. 26). 



"Nothing is, perhaps, better 

 calculated to excite the admira- 

 tion of the student of animated 

 nature, than the amazing- results 

 produced by the slightest devia- 

 tions from a common type of 

 organization ; and in examining 

 the changes required in order to 

 metamorphose an organ which 

 we have already seen perform- 

 ing such a variety of offices into 

 fins adapted to an aquatic life, 

 this circumstance must strike 

 the mind of the most heedless 

 observer. The limbs used in 

 swimming exhibit the same 

 parts, the same number of joints, and almost the 

 same shape, as those employed for creeping, climb- 

 ing, leaping, and numerous other purposes ; yet 

 how different is the function assigned to them ! 

 In the common water-beetle (fig. 26) the two 

 anterior pairs of legs, that could be of small ser- 

 vice as instruments of propulsion, are so small as to appear quite dispropor 

 tionate to the size of the insect, while the hinder pair are 

 of great size and strength ; the last-mentioned limbs are, 

 moreover, removed as far backwards as possible by the 

 development of the hinder segment, of the thorax, in 

 order to approximate their origins to the centre of the 

 body, and the individual segments composing them are 

 broad and compressed, so as to present an extensive sur- 

 face to the water, which is still further enlarged by the 

 presence of flat spines, appended to the end of the tibia, 

 as well as of a broad fringe of stiff hairs inserted all 

 around the tarsus. The powerful oars thus formed can 

 open until they form right angles with the axis of the 

 body, and from the strength of their stroke are well adapt- 

 ed to the piratical habits of their possessors, who wage successful war, not 

 only with other aquatic insects and worms, but even with small fishes, the 

 co-inhabitants of the ponds wherein they live." T. Rymer Jones. 



16. Other coleop'terous Pentame'rans, which have but two palpi 

 on the maxillae, and filiform or saw-like antennse, belong to the 

 family of Ser'ricornes (from the Latin, serra, a saw, and cornv, 

 horn), are worthy attention. 



17. Of this number are the fire-flies Elater (from the Greek, 

 elater, a leaper), which have the power of leaping when placed on 

 the back. If a beetle be seen to fall upon its back, and instead 

 of making the ordinary efforts to set itself on its legs, bends its 



16 How is the family of Ser'ricornes characterized ? 

 17. What arc the habits of fire-flies? 



Fig. 26. 



V7ATER- BEETLE. 



