432 R. 1. POOOCK. 



EXPLANATION OF FIGURE OPPOSITE. 



Diagram to illustrate the homology of the metameres in 

 Chilopoda of the Scolopendroid, Craterostigmoid, Litho- 

 bioid, and Scutigeroid types. 



Letteking and Numbeking fok all Figures. 



at. A.iiteiina. c. Cephalite. b. Basal plate =^ ter^um of somit.e-beariug 

 toxicognatli. t. Toxicoguath, p. Palpognatli. 1—21, 1 — 15, 1 — 8. Terga 

 of leg-bearing somites. 1' — 21', 1' — 15'. Sterna of leg-bearing somites. 

 g. Genital somite, a. Anal somite. 



A. Hypothetical primitive Scolopendroid willi twenty-one subequal stigma- 

 tiferous somites, with gonopods on the genital somite {g.), a distinct tergal 

 plate {b) on the somite bearing the toxicognaths, and with the penultimate 

 and antepenultimate segments complete on the post-axial side of this appen- 

 dage. 



B. Typical Scolopendroid, resembling Rhysida, derivable from A by the 

 restriction of the stigmata to the somites numbered 3, 5, 7, 8, 10, 12, 14, 16, 

 18, 20 ; by the incipient differentiation of the leg-bearing somites into major 

 stigmatiferous and minor astigmous ; by the suppression of the gonopods ; 

 and by the obliteration of the tergum of the toxicoguath and of the penulti- 

 mate and antepenultimate segments of this appendage on its post-axial side. 

 This figure also shows the juxtaposition of the two major somites numbered 7 

 and 8. 



C. Diagram of Craterostigmus to show its derivation from A by the 

 restriction of the stigmata to the somites numbered on the dorsal side 4, 7, 

 12, 15, 18, 20, and by the excalation of the sternal area and appendages of 

 the somites numbered 3, 6, 9, 11, 14, 17; also by the coalescence of the 

 elements of the genital and anal somites to form a bivalvular capsule {a +g). 



U. Typical Lilhobioid, resembling He ni cops, derivable from C by the 

 completion of the excalation of the half-somites in C numbered on the dorsal 

 side 3, 6, 9, 11, 14, and 17, but retaining the distinctness of the genital and 

 anal somites and the stigmata upon the first leg-bearing somite, as in A. Tliis 

 figure also shows the alternation of major stigmatiferous and minor astigmous 

 somites, the juxtaposition of the two major somites, 7 and 8, and the chaiijje 

 of the major somites from tiie odd to tiie even numbers in the posterior half 

 of the body. 



E. Dia"-ram of Scutigera to show its descent from a Lithobioid of the 

 Henicops type (D) by the dorsal migration and fusion of the stigmata; by 

 the enlargement of the stigma-bearing tergal plates, their backward extension 

 over, and almost complete obliteration of, the terga of tlie minor somites 

 represented ventrally by the sterna numbered 2', 4', 6', 9', 11', 13', and by the 

 fusion of the terga of the seventh and eighth somites to form a siugle plate 

 (J.) — t,he two processes resulting in the presence of eight visible tergal plates 

 instead of fifteen. This figure also shows the widely separated antennae, the 

 polymeniscous eye, the large projecting prseantennal area of the cephalite, the 

 long and pediform palpognalh and partially rotated toxicognatli, characters in 

 which Scutigera differs from all known Chilopods. 



