330 Froceedings of the Royal Irish Academy. 



There is good reason, therefore, for considering that the richly- 

 segmented Centipedes are abnormal developments from forms Tvith a 

 moderate number of segments. The palseontological evidence of the 

 subject is very meagre. In Carboniferous times, vre knoiv from the 

 researches of Scudder ('90) that Latzelia, a form resembling Scutigera, 

 but without the specialised dorsal tracheal system, existed. The 

 fossils referred by Scudder to the Eoscolopendridfe are too imperfect 

 for any certain conclusions to be drawn from them. If the bristle- 

 bearing animal Palteocampa, referred by him to a special order, the 

 Protosyngnatha, were indeed a Centipede, its body-segments were biit 

 few in number. Embiyological researches on the Centipedes, the 

 latest of which is Heymons' exhaustive treatise on the development of 

 Scolopendra ('01), show the close correspondence between the Chilopodan 

 and the Insectan head. The presence of a tritocerebral rudiment in 

 the Centipedes has been established, so that the feelers, mandibles, 

 maxillae, maxillulse, and labium of the insect correspond respectively 

 with the feelers, mandibles, two pairs of maxillae, and poison-jaws of 

 the Centipede. The freedom from the head of the segment bearing 

 the last-named limbs in the Centipedes shows that their ancestors must 

 have diverged from the primitive stock at a very early period. In 

 this respect, the head of Scolopendrella is specialised as compared with 

 the Centipede-head ; and in the Symphylan ancestral stock of Centi- 

 pedes and Insects, the pair of limbs that now fonns the plate-like 

 labium in Scolopendrella and the CoUembola, must have been fi-ee and 

 leg-like. 



One of Heymons' most startling discoveries is the presence of a 

 pair of pre-antennal rudimentary appendages on the head of the 

 Scolopendroid embryo. The segment bearing these he regards as post- 

 oral ; and he ranges it with the optic segment of the insect head. Its 

 existence strongly suggests that the eyes of the far-ofi ancestors of 

 Centipedes were stalked and appendicular. As the development of 

 the lateral simple eyes in Scolopendra does not support the theoiy that 

 they are degraded compound eyes, it is to be presumed that the ances- 

 tral compound eyes have been lost, except in the Scutigeridae. 



Turning next to consider the Millipedes, we find that they, like 

 Centipedes, exhibit a wide divergence in their segmentation. It is 

 impossible to lay any stress on the hexapod condition of their larvse, 

 as indicating relationship to the Insects, as the segments on which the 

 three pairs of legs occur are not successive, and vary in different 

 groups. But the strongest evidence for the derivation of the Diplopoda 

 from the same stock as the Chilopoda and the Insecta is afforded by 



