A Monograph of Scytonotus. 245 



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19th and 20th than on the other legs, this being allowed by the 

 conformation of the third and fourth joints. 



10. On the posterior face of the distal part of the fifth joint of 

 the loth-18th legs is a protuberance, very large and curved on 

 the loth, graduallj^ smaller on the 14th, 15th, 16th and ITth, in- 

 conspicuous or wanting on the 18th. 



11. Rising from the anterior face of the distal part of the 19th 

 and 20th legs is a similar large protuberance. 



12. On the ventral side of the sixth joint of all the legs except 

 the 1st and 2d pairs there are three or more rows of 11-14 coarse, 

 rounded, conic teeth, each of which is extended on the distal side 

 into a long bristle. Similar structures occur on the males of 

 Polydesmus, the tubercles being lai-ger and less numerous. 



Secondary Sexual Characters of Females. 



1. The coxa? of 2d pair of legs are ventrally inflated and densely 

 papillose, and are separated by a median prolongation of the 

 pedigerous lamina. 



2. The pedigerous lamina is prolonged between the legs of the 

 third pair, and is medianl^' deeph' lobed and papillose. 



3. The first, second and third joints of all the legs are more or 

 less papillose on the dorsal face, the papillae being more and more 

 obscure on the legs of the last few segments. 



4. The carinse of segments eight and nine, and usualh' of one 

 or two adjacent segments are much reduced or entirely wanting, 

 causing the female to appear much more slender. The reduction 

 or absence of cariuae is no doubt correlated with the special modi- 

 fication of the 13th and immediately following legs of the male, 

 for in copulation these legs clasp the segments mentioned. 



The above secondary differences between the sexes are in many 

 respects the greatest known to occur in the present sub-class. 

 The genitalia of Polydesmidse are, of course, much less complex 

 than those of the other families of the Helminthomorpous group, 

 but one pair of le2;s being transformed for this purpose, while in 

 the lulidaj two are used, and in the Chordeumidte sometimes as 

 many as four pairs. In the Chordeumidie, also, the secondary 

 modifications are in some cases very considerable, but are almost 

 entirely confined to the legs in front of the genitalia, and special 

 adaptations of legs far behind the genitalia do not appear. It is. 



