Appendages in Hexapoda. 203 



organs by their being paired, as also by their rather ventral 

 position on each side of the intestine, show a primitive con- 

 dition, their opening in an unpaired slit *, placed behind the 

 third pair of legs, appears to be of secondary origin. 



The order Chilopoda also, as already urged by V. Graber 

 and the author in opposition to F. Brauer, is above all ex- 

 cluded from being regarded as a direct ancestor of the Insecta, 

 by the decided drawing up of the first pair of legs to form 

 part of the mouth-organs, and, further, the asymmetrical 

 development of the dorsally-placed sexual organs is to be 

 regarded as secondary, although their aperture, situated close 

 in front of the anus, shows the original type, still represented 

 by the Annelid-like Peripatus. 



To decide the question whether the postembryonal increase 

 from 9 or 7 to 17 f or 13 leg-bearing segments common to 

 the Chilopoda Anamorpha (e. g. Lithobius) and Scolopendrella 

 is to be regarded as a phyletic repetition, or, as is more pro- 

 bable, as a secondary larval phenomenon, our knowledge is 

 still insufficient ; at any rate, in Scolopendrella the gemmipa- 

 rous zone is situated in front of the subsequent thirteenth pair, 

 and therefore, as in the Chilopoda, immediately before the 

 preanal segment, and the insertion of new somites occurs from 

 before backward, so that in both the hindmost pair of ambu- 

 latory legs is also the youngest. 



The order Diplopoda stands in the closest relation to Sco- 

 lopendrella by the intimate fusion of the last two pairs of jaws 

 into a gnathochilarium, which appears as a simple appen- 

 dage even in the first embryonic rudiment, and by the anterior, 

 although separated, opening of their paired and decidedly 

 ventrally-situated genital sacs (behind the second pair of 

 legs) ; and their apparently double segments are to be 

 accounted for by the union of two individual segments 

 effected by the fusion of their dorsal plates, as demonstrated 

 by Newport and since, among others, by the author, Latzel, 

 and, recently, Heathcote. In point of fact the resemblance 

 of the embryo lulus to an insect-larva, which is so often 

 referred to, is also so far purely superficial, that one of the 

 thoracic segments J has no appendage, and consequently the 

 * Successful serial transverse sections now enable me to confirm the 

 union of the germ-sacs with the anterior unpaired slit, as stated by B. 

 Grassi in 1884, in both sexes. 



t In the Chilopoda referred to the poison-gland segment and also the 

 preanal genital segment, which also bears jointed appendages, are inclu- 

 ded in the number 17. 



X By analogy with Scolopendrella nothacantha, Latz. & Haase ( = Isa- 

 bella, Grassi), and Pauropus, and in accordance with Heathcote 's view 

 (Phil. Trans, vol. clxxix. (1888) p. 159), we must regard thejirst thoracic 

 segment as the footless one. 



16* 



