216 FKESH-WATBE AQUAEIA. 



Gyrinus. They may be seen keeping up their lively gyrations 

 on the surface of almost any pond or sheltered nook of 

 many a stream during nearly every fine and mild day 

 throughout the year. Their habit of continually moving in 

 either curves or circles has given them the generic name of 

 Gyrinus, and the more familiar ones of " Whirligigs " and 

 "Whirlwigs," and the sheen of their elytra has also caused 

 them to be called, most appropriately, "Shiners.'' These 

 beetles are gregarious, and are generally seen together in 

 numbers ranging from ten to thirty, and this custom of 

 theirs should be remembered by those who intend to keep 

 them in confinement. The genus Gyrinus contains about five 

 British species, the members of which are in shape either 

 ovate or oblong-ovate, and in size vary from ^in. to a little 

 more than Jin. Their elytra, which are very glossy and are 

 turned a little under the body at their edges, do not reach to 

 the apex of the abdomen, and their antennae are short and 

 thick. It will be noticed that the posterior legs of most 

 other aquatic beetles are the longest ; but in the case of the 

 Gyrinidse the anterior legs are of the greatest length, while 

 their others are very short and strong, and at the extremities 

 rather fin-Hke. The " Whirligigs '' use their long fore- 

 legs for seizing and holding their prey, and also, it is said, for 

 directing their way upon the surface of the water. The eyes 

 of these insects are most curious and interesting. Each eye, 

 so to speak, is divided into two by a partition, in which an 

 antenna' is fixed. The upper of the two eyes thus formed is 

 used for looking at objects above the surface of the water, 

 and the lower for those beneath it. This accounts for their 

 extraordinary quickness of sight, which anyone can prove for 

 himself by trying to catch them in a net. These active and 

 alert little beetles dive under the water at the sEghtest ap- 

 pearance of danger from above, often coming up again 

 beneath some flat floating leaves. They will also thus hide 

 below pieces of paper placed upon the surface of the water of 

 the aquarium. 



The Gyrinidse are very good flyers, and therefore the 

 tank in which they ai-e confined shoidd be carefully covered. 



