Cakpentek — RelationaJiipH between Clauses of Arthropuda. G-'Jl 



the fact that in Scolopendrella the genital opening is far forward, as 

 in the Millipedes, while the curious group of the Pauropoda, which show 

 many points of correspondence with the Symphyla, have been proved 

 to exhibit (Kenyon, '95) marked Diplopod affinities. Kenyon, indeed, 

 places the Pauropoda, together with the Pselaphognatha (Polyxenidaj), 

 in a group which he calls the Protodiplopoda. Pauropus has only 

 nine pairs of legs ; and its segments are imperfectly fused. There can 

 be little doubt that this form has undergone secondary shortening; but 

 Polyxenus has thirteen leg-bearing segments followed by two limbless 

 segments, so that its segmentation agrees exactly with that of 

 Scolopendi'ella and the primitive Insects. The mandibles of Paui-o- 

 pus and Polyxenus resemble those of the Collembola. In other 

 Millipedes, these jaws are complex, being composed of several sclerites 

 — a condition which, like that of the mandibles in certain Scarabaeid 

 beetles, must perhaps be regarded as a secondary adaptation. The 

 ^* lower lip " or " gnathocilarium " of Millipedes seems to be certainly 

 formed by the union of two pairs of appendages which probably 

 represent the maxillulse and maxillae of Insects ; while the labial seg- 

 ment of Insects is represented by an embryonic limbless segment 

 (Heymons, '97). (See Table, pp. 354-5.) 



What palseontological evidence we possess of the history of Milli- 

 pedes shows that richly- segmented forms, in which the segments were 

 already beginning to fuse together in couples, were living in Devonian 

 times. But as winged Insects have been traced back to the Silurian, 

 we have nothing but comparative studies in living forms to guide us 

 us to the nature of the common ancestor of Insects and Millipedes. 

 Morphological evidence shows clearly that Millipedes might well have 

 arisen, through some form combining the primitive characters of 

 Pauropus and Polyxenus, from a Scolopendrelloid stock. The fusion 

 of segments in couples would not be likely to take place until the 

 number of segments had become very great. It is suggestive to notice 

 in this connexion that, in the Pauropoda and Pselaphognatha, the 

 fusion of segments has hardly begun. The earliest truly " diplo- 

 podous " forms would have been elongate Juloid Millipedes. Thence, 

 by a reduction in the number of segments, the Glomeroid forms may 

 have sprung. 



The difficulty that arises in bringing together two groups which, like 

 the Millipedes on the one hand, and the Insects'and Centipedes on the 

 other, exhibit a great difference in the position of the genital apertm-e, 

 will be discussed later in connexion with the relationship between 

 Insects and Crustacea. For the present it is enough to repeat the 



