296 THE SCHOOL OF Rl^AUMUR 



were attempted in French, Dutch, and English ; all but 

 one of them remained imperfect. Schwartz published 

 a Nomenclator, in which modern names are given to 

 the figures. Roesel's original drawings are still pre- 

 served. 



Aquatic Beetles 



Roesel begins his account of the water-insects with 

 the Dytiscus family, and Dytiscus marginalis is his first 

 example. He employs no scientific nomenclature, and 

 merely distinguishes two " genera " of water-beetles, viz., 

 the flattened forms and those with prominent rounded 

 back ; then he goes on at once to the species, for which 

 he has no accepted names, either Latin or German. The 

 Q,gg, larva, pupa, and imago of Dytiscus marginalis are 

 described and figured ; the changes of the larval skin 

 and other minute particulars of the life-history are 

 pointed out. So unfamiliar at that time were the 

 habits of a Dytiscus that Roesel had at first no notion 

 what to feed his captive larvae upon. Nevertheless he 

 remarks many things which might have escaped a less 

 attentive observer ; he knows for instance that the 

 larva comes up to the surface to breathe, and hangs 

 head downwards by a pair of tail-projections. He 

 watched the capture of a victim, and the sucking of its 

 juices, though he does not mention the perforated 

 mandible. Frisch taught him that the larva quits the 

 water before pupating, but he had to learn by experience 

 that the earth into which it retreats must be damp. He 

 knows the marks of the sexes, and gives an excellent 

 account of the suckers on the forelegs of the male. On 

 the whole the description is quite as good as that given 

 in most popular books of our own day, but the figures 

 are much better than those which we are accustomed 

 to see. 



