54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



while in Scolopcndroniorpha there are either 26 or 28 l)ody segments, 

 but the number is constant for each species. 



The gonads of the Chilopoda lie above the alimentary canal, as in 

 Crustacea and Hexapoda, whereas in the progoneate myriapods they 

 lie below the alimentary canal. The testes in Epimorpha consist of 

 from I to 12 pairs of short spindle-shaped tubes each united at each 

 end by a slender ductule with a common median gonoduct. Among 

 the Anamorpha, LitJiobius has a single median tubular testis, but 

 Scutigera has two slender testicular tubes. The ovaries are in all 

 forms united in a single median tubular gonad, in the walls of which 

 the germ cells are arranged in a longitudinal band or a pair of lateral 

 bands. The median gonoduct of each sex is apparently a ductus con- 

 junctus ; posteriorly it divides into two arms that embrace the rectum 

 and unite again below it in a short exit or genital chamber, into which 

 open one or two pairs of accessory glands, and in the female a pair 

 of seminal receptacles. The left branch of the gonoduct in the Epi- 

 morpha becomes reduced or rudimentary, and only the right branch 

 serves as the functional exit tube. 



The external genital region of the chilopod body consists of two 

 small legless segments intercalated between the last leg-bearing seg- 

 ment and the terminal anus-bearing telson. These segments, which 

 in the Epimorpha are differentiated during embryonic development as 

 two very small somites (fig. 20 A), are termed by Heymons (1901) 

 the pregenital segment (igSeg) and the genital segment (2gSeg). 

 The two segments may bear each a pair of small or rudimentary ap- 

 pendages, which are the first and the second gonopods {iGp, 2Gp). 

 The definitive genital opening is formed behind the sternum of the 

 genital segment ; the gonopore is usually concealed in a genital cham- 

 ber, but in the male it is on a small protractile penis. In the Ana- 

 morpha, which add segments during postembryonic development from 

 a generative zone before the telson, the genital segments are the last 

 to be formed. The definitive segmentation of the chilopod body, there- 

 fore, depends on the number of somites generated before the estab- 

 lishment of the genital segments, after which there is no further 

 somite propagation. The variable number of pregenital segments 

 generated in the Chilopoda from a postgenital zone of growth, as 

 already noted, must lead to the conclusion that the two segments in 

 the definitive genital region are not homologous somites in all cases, 

 notwithstanding their similarity of structure. However, the structure 

 of these two segments is probably only that which any segments might 

 take on if arrested in their growth at an early stage of development. 



The most generalized condition of the genital region in the adult 

 chilopod is found in the Geophilomorpha, in which both genital sterna 



