686 EXTERNAL ANATOMY OF INSECTS. 



Monomerous insects are those which have only a single 

 tarsal joint. Only one Coleopterous and also one He- 

 mipterous genus is so distinguished : the first is Der- 

 mestes Armadillus De Geer a , and the second the common 

 water-scorpion, Nepa Latr. Among the Apt era we 

 find Nirmus, Podura, Sminthurus, &c, that belong to this 

 section. 



To the above sections another may be added for those 

 insects whose tarsi have more than/ue joints, which may 

 be denominated Polymerous. Here belong the genera 

 Gonyleptes K., Phalangium and Scutigera Latr. In the 

 first the number of joints varies from six to eleven, and 

 in the two last they far exceed that number, amounting 

 in some species of Phalangium to more than Jifty, and 

 becoming convolute like the antennae of Ichneumons b . 



I am next to notice the proportions and shape of the 

 tarsus and its joints. The most general law is, that it 

 shall be shorter and more slender than the tibia ; but it 

 admits of several exceptions — thus, in Megasoma K. c , in 

 all the legs; in Agrostiphila M C L. MS. d in the inter-* 

 mediate, and in Amphicoma lineata in the posterior pair 

 the tarsi are the longest ; in Trichius Delta these last 

 are longer than the thigh and tibia together. In some 

 insects the tarsi are disproportionally short, as in Cas- 

 sida, the Pselaphidce, Locusta Leach, &c. Though ge- 

 nerally more slender than the tibia, in several instances 



a From De Geer's description this insect seems related to Agathi- 

 dium (iv. 221 — . t. viii./. 21—23). M. Leclerck de Laval discovered 

 it to be monomerous. Regne Animal, iii. 365. 



b Plate XXVII. Fig. 22. c See above, p. 311. Note a. 



•' Melokmtha sericea and aurulenta. Linn. Trans, xii. 463. 400. be- 

 long to this subgenus. 



