TYPE THACHEATA. 



525 



It .will be seen from this that in the Diplopoda the arrangement is 

 intermediate between that found in Peripatus and that of the Chilopoda, 

 while these latter approach closely the Insecta, and this seems to be the ac- 

 tual relationship, Scolopendrella forming an intermediate link between the 

 Chilopods and the Insecta, approaching the Thysanura closely in the ar- 

 rangement of the mouth-parts and in the number of segments of which the 

 body is composed. The Diplopoda, it is true, pass through a larval stage in 

 which but six legs are present, and it might at first sight be supposed that 

 this indicates an affinity with the Insecta, but these legs do not belong to 

 the same segments as do those of the Insects, and furthermore the occur- 

 rence of rudimentary abdominal appendages in some Thysanura, as well as 

 in the embryonic stages of probably all Pterygota, indicates that the In- 

 secta have been derived immediately from forms with many pairs of appen- 

 dages, and these forms seem to be represented most accurately by the exist- 

 ing Scolopendrella. 



SUBKINGDOM METAZOA. 

 TYPE TRACHEATA. 



I. Class PROTRACHEATA. Annelid-like forms ; trunk not differentiated 



into thorax and abdomen ; with nephridia. Peripatus. 

 II. Class MYRIAPODA. Elongated forms; trunk not differentiated into 

 thorax and abdomen ; posterior trunk-segments with appen- 

 dages in the adult. 



1. Order Pauropoda. Small forms ; with only one pair of maxillae ; 



antennae ending in three flagella ; reproductive orifices at basis 

 of second pair of trunk-appendages. Pauropus, Enrypauropiis. 



2. Order Diplopoda. With only one pair of maxillae ; antennas 



simple ; reproductive orifice on second or between second and 

 third trunk-segments ; most of the trunk-segments with two 

 pairs of legs. lulus, Lysiopetalum, Polydesmus, Strongylo- 

 so ma, Glomeris. 



3. Order Chilopoda. With two pairs of maxillae and with maxillipeds; 



antennae simple; reproductive orifice on the antepenultimate 

 segment ; each trunk-segment with a single pair of legs. 

 Cfeophiliis, ticolupendra, Lit/iobius, Scutiyera. 



