552 PROCEEDIXGi^ OF THE XATTOXAL Mrf^EFM. vol. xxxvi. 



These points are simply suggestive and it is not claimed that a 

 close relation necessarily exists between the Chilopoda and the 

 Hexapoda. Verhoeff (1903), hoAvever, goes further than this and 

 identifies l)oth the episternum (coxopleure) and epimerum (anopleure) 

 with separate i:)lates of the chilopod pleurum. 



p.. ITkxai'oda. 



I. APTF.KA. 



Since the importance of this order is philosophical rather than 

 practical, the author has not devoted much lime to its study. More- 

 over the external anatomy of the thorax in the three princij:>al genera 

 has been thoroughl}^ exploited bv Verhoetf (1903, lUO-ta). 



As is well known, the Japygida^ possess a small intercalary tergal 

 plate between the pronotum and the mesonotum and another between 

 the latter and the metanotum. V>y many authors these are regarded 

 as I'udiments of ])rimitive segments and the primitive thorax is con- 

 ceived to have been comjjosed of three pairs of segments described 

 and named by Verhoetf (l!)03c, 190-la) as follows: The microthorax 

 and prothorax, the stenothorax and mesothorax, and the cryptothorax 

 and metathorax. But this subject has been discussed in Section IT, 

 dealing with the segmentation of the head and body (p. 519). 



Yerhoetf (1903) describes the pleura of all three segments of Japyx 

 as very similar to the pleurum of Lithohius. He shows in L. forficatus, 

 however, two plates al)ove the one attached to the coxa (22, P?) in- 

 stead of one as shown by the species figured in this paper (22). The 

 microthorax is represented by a sternal plate only. In Lej)is)7ia, ac- 

 cording to Verhoetf, the prothoracic pleura have all the parts of the 

 pleura of Blattidiv and Euplexoptera (Dermaptera), l)ut the parts 

 are rudimefitary in the mesoUiorax and the metathorax. The micro- 

 thorax in this genus, also, consists of a large sternum but has no 

 pleural or tergal plates. In Machilis the three segments differ much 

 from those of either Japyx or Lepisma. The microthoracic sclerites 

 and the pleurites of the other three segments are almost lacking, 

 while the terga are largely developed and reach far down on the 

 sides of the thorax. 



In Japyx each thoracic segment bears a spiracle, while a fourth 

 spiracle is present close to the lateral margin of the mesosternum 

 and near its posterior edge. Hence, this spiracle nuist be the spiracle 

 of a degenerate segment. 



Verhoeff' (1903) regards the Thysanura not as insect " progenitori," 

 but as a degenerate residiuiry branch of the primitive wingless in- 

 sects. This view is un(l()ul)tedl3' the correct one. 



