NO. 14 INSECT ABDOMEN SNODGRASS 53 



consists of two segments, a basal coxopodite (Cxpd), and a distal 

 telopodite {TIpd). The essential feature of the organ is a sperm 

 receptacle (r), which is an invagination cavity on the morphologically 

 anterior surface of the coxopodite, and a sperm canal (c), which is 

 usually a closed groove that traverses the telopodite from the sperm 

 receptacle to the apex of the appendage. The coxopodite is generally 

 provided with a movable endite lobe (Cxnd) of various shapes, which 

 projects over the sperm receptacle, and when slender may be partly 

 inserted into the proximal opening of the sperm canal. The bases of 

 the appendages are often sunken into a deep cavity on the ventral 

 surface of the body segment (D). The gonopods are subject to end- 

 less modifications in form, and their structural diversity in different 

 genera and species furnishes valuable characters in diplopod taxonomy. 

 An example of gonopods having a highly diversified and complex 

 structure is shown in the genus Thyropygus (fig. 19 G, I). A very 

 much simplified structure, on the other hand, is found in Habro- 

 strepus (B), in which the telopodite (Tlpd) of each gonopod has 

 the form of a short broad lobe with a wide, basinlike sperm cavity 

 (r) on its ventral anterior surface, which is partly covered by a flat 

 endite lobe (Cxi) of the coxa. In some forms, as in Parajtdus 

 (L, M), both pairs of legs of the seventh body segment are trans- 

 formed into gonopods, the second of which in this case contain the 

 sperm receptacles (M, r) and canals (c). More extensive and de- 

 tailed descriptions of the diplopod gonopods will be found in works 

 by Vosges (1878), Verhoeff (1903), Silvestri (1916), Attems (1894, 

 1926), and Siefert (1932) ; the last writer gives also an account of 

 the manner of copulation and insemination in Polydesmus edentidus. 



IX. CHILOPODA (MYRIAPODA OPISTHOGONEATA) 



The Chilopoda have a single median genital aperture, which in 

 each sex is always behind the sternum of the last somite, that is, 

 between the penultimate body segment and the anus-bearing end seg- 

 ment, or telson. The number of segments anterior to the genital 

 segment, however, is so variable in the chilopods as a whole that no 

 fixed numerical designation can be given to the genital segment itself. 

 In the anamorphic forms (Lifhobius, Scutigera), in which the adult 

 segmentation does not vary, there are 19 definitive body segments, 

 including the telson. Counting four postoral somites in the head, the 

 genital segment in this group, therefore, is somite XXII . Among the 

 Epimorpha, in which the definitive segmentation is in most forms 

 complete at hatching, the number of segments is highly variable in 

 the Geophilomorpha, even in the same species, and may be very large, 



