6S1 EXTERNAL ANATOMY OF INSECTS. 



thus reversing the number in the preceding tribe : other 

 Heteromerous genera are to be found amongst the He- 

 miptera. Thus, in Ranatra the numbers are 2. 1.1.; in 

 Sigara and Nauceris 1:2:2; in a new subgenus between 

 Belosloma and Naucoris (Xiphostoma K. MS.), brought 

 by Dr. Bigsby from Canada, 3:2:2: in the Lepidoptcra 

 the butterflies called tetrapi (Vanessa, &c.) may be ex- 

 pressed by 1:5:5. Amongst the Aptera and Arachnida 

 there are three remarkable genera, which if their pedi- 

 palps are included may be deemed Heteromerous. I 

 mean Phrynus, Thelyphcna, and Galeodes ; — in the for- 

 mer the numbers will be * : 4 : 4 : 4, the asterisk denoting 

 more than ten ; in the second, 8:4:4:4.; and in Gale- 

 odes) in which the first pair of pedipalps are not chelate, 

 the mandibles performing their office) the numbers are 

 l:l:3:3:3. a 



Tetramerous insects are those in which all the tarsi 

 consist of four joints ; these in the Coleoplera are next in 

 number to the pentamerous — indeed a very large propor- 

 tion of them strictly speaking are really of the latter 

 description, since in Linne's four great genera, Curctdio, 

 Cerambyx, Chrysomela, and Cassida and some others, 

 the claw-joint (ungula) consists of two articulations, one 

 very short, forming merely the ball at its base b , which 

 inosculates in the socket of the preceding joint, and the 

 other constituting the remainder : if you carefully sepa- 

 rate these two pieces, you will find that the last inoscu- 



' A These three genera appear really to have only six legs, since the 

 pedipalps or maxillary legs are not armed with claws, while the 

 real representatives of the legs, or three last pair, are so distin- 

 guished. In Phrynus and Thelyphona the anterior pair are chelate ; 

 but in Galeodes they are pediform, as in the Araneidce, and the great 

 chela; are the mandibles. >> Plate XXVI. Fi.g, 47, 48. d *. 



