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INTRODUCTION TO ZOOLOGY 



to be seen clinging to the end of the body. The two back 

 pairs of legs are short but broad, fringed with hairs, and are 

 used in swimming, the front pair being 

 used for holding. In the male the tarsal 

 joints are enlarged. 



These beetles feed on water plants 

 and minute water insects, and they hiber- 

 nate on the mud at the pond bottom. 

 Eggs are laid in the spring on some sub- 

 merged plant, and the larvae hatch within 

 a fortnight ; they may be but little more 

 than half an inch long, and each has a 

 head and twelve segments. The three 

 thoracic segments bear ordinary jointed 

 legs, and each of the first eight abdominal 

 segments bears a pair of delicate feathered 

 "tracheal gills," while the last segment 

 bears two pairs of such gills. The larva 

 is carnivorous, but will at times feed on 

 water plants. It swims actively with a 

 serpentine motion. After a while it 

 leaves the water, and is said to pupate on 

 some plant which grows above the water surface, spinning 

 for itself a little silk cocoon well hidden amongst the foliage 

 and very rarely seen. The imago emerges in August or 

 September. 



Fig. 188.— The Larva 

 of the Whirligig 

 Beetle. 



Sub -order 3 : Serricomia. 



Garden Beetles with Serrate Antennae. 



In the family of the Skipjacks, or Click Beetles 

 Click Beetles (■^^*'^"^**)> the form of the antennae is very 

 variable. It may be serrate — made up of little 

 triangular pieces, which project most on the inner side of the 

 antenna — but it is thread-like in just a few beetles which, how- 

 ever, because of their resemblance in other points, are also 

 classed here. A curious feature in the anatomy of Click 

 Beetles is the elongation of the first segment of the thorax on 

 its under side into a central spine (Fig. 189, s), which points 

 backwards and fits into a groove in the second segment. 

 If the beetle is put on its back, it arches up its body 



