COLEOPTERA. — GYRINIDJE. 107 



femora and tibiae being trigonate, the latter with short flattish cilia; at 

 the external apical angle, and with the three basal joints of the tarsi 

 (which are 5-jointed) produced on the inside into long, flat, ciliated 

 leaf-like lobes ; the fourth joint is of similar size and form ; but the 

 terminal joint, which is very short, is attached near the extremity of 

 the latter, the intermediate tarsi being provided with a pair of short 

 ungnes, and the posterior pair having only a single and almost ob- 

 solete claw; the anterior tarsi are large and dilated, with two strong 

 claws, the male tarsi being flat beneath, and covered with numerous 

 minute granulations and margined with a minutely serrated cilia. The 

 hind legs are very transparent, presenting an excellent object for the 

 microscope, exhibiting very distinctly the circulatory system in nu- 

 merous convoluted veins. From the apparently equal action of the 

 two posterior pairs of legs, the meso- and metasternums are nearly of 

 equal size, the posterior coxa; being very greatly enlarged {fig. 6. 7.). 



These beetles are almost the only water insects which exhibit a bril- 

 liant metallic lustre, a peculiarity dependent upon the habits of the 

 insects which generally swim upon the surface of the water. 



With the exception of a few exotic genera, the Gyrinidas are of a 

 small size, not exceeding one third of an inch in length, the largest 

 even not being one inch long. 



These insects cannot fail to have attracted the attention of every 

 person when passing near standing, or gently running, water, on the 

 surface of which they are to be seen in groups, varying in number from 

 a couple to several hundreds, whirling about in every direction, but 

 generally in circles, whence they have obtained the English 'name of 

 Whirlwigs, and the French one of tourniquets. When thus occupied, 

 their motions are so exceedingly quick, that the eye is perplexed in 

 following them, and dazzled by the brilliancy of their wing cases which 

 glitter like bits of polished silver or burnished pearl. These dances 

 are kept up throughout the year, even during the winter, as the insects 

 may be thus observed on fine days, whenever the water is not covered 

 with ice. It has indeed been said that they retire in the autumn and 

 repose in a dormant state during the latter season, attached to the 

 roots of aquatic plants, or in the mud at the bottom of the water : on 

 approaching them, they instantly take alarm, and dive beneath the 

 surface, carrying with them a little bubble of air, which glitters like a 

 drop of quicksilver, and is attached to the posterior portion of their 

 bodies. Sometimes they may be taken flying, their large wings en- 



