322 INSECTA. 



ration of a similar period, and the animal is then double its former 

 size. Its final length is two inches. They have been observed, in 

 summer, to enter into their pupa state at the end of fifteen days, and 

 to become perfect insects in fifteen or twenty more. Besides the 

 cloaca of the Insects of this family, the Dytisci have a tolerably long 

 caecum, which is perceptible even in the larva 



This great genus is subdivided as follows: 



Some have antennae composed of eleven distinct joints, the exte- 

 rior palpi filiform or somewhat larger at the extremity, and the base 

 of their posterior feet as well as that of the others exposed. 



Sometimes the thickness of the antennae gradually diminishes 

 from their origin to the extremity; the last joint of the labial palpi 

 is simply obtuse at the end and unemarginate. Such is 



Dytiscus, proper. 



Where all the tarsi are composed of five very distinct joints, of 

 which the three first of the two anterior ones are very wide, forming, 

 collectively, a palette, either oval and transverse, or orbicular. 



D. latissimus, L.j Panz. Faun. Insect. Germ. LXXXVI, 1. 

 About an inch and a half long, and easily distinguished by the 

 compressed and trenchant dilatation of the exterior margin of 

 the elytra, the border of which is yellowish; thorax margined 

 all round with the same colour; elytra sulcated and carinated 

 in the female. From the department of Vosges in the north 

 of Europe and from Germany. 



D. marginalis, L. ; Panz. lb. 3. About a fourth smaller; a 

 yellowish border all round the thorax, and a line of the same 

 colour on the exterior and non-dilated margin of the elytra; 

 those of the female sulcated from their base to about two-thirds 

 of their length. 



Fabricius says that if laid on its back, it soon regains its nat- 

 ural position by jumping. 



Esper preserved a D. marginalis for three years and a half, in 

 perfect health, in a large glass jar. Every week, and some- 

 times oftener, he threw into the vessel a piece of raw beef about 

 the size of a filbert, on which it darted with great avidity, and 

 then completely exhausted its blood by suction. It can go with- 

 out food for at least four weeks. It kills the Hydrophilus pi- 

 ceus, although double its own size, by piercing it between the 

 head and thorax, the only part of the body that is unarmed. 

 According to Esper, it is affected by atmospheric changes, and 

 indicates them by the height at which it remains in the jar. 

 D. Roeselii, Fab.; Roes., Insect., II, Aquat., Class I, ii. Nar- 



