METAZOA MYRIAPODA. 385 



A metamorphosis is correlated with this immaturity, as 

 we have seen in other groups of the animal kingdom. 

 The larval stage seems to be adaptive and therefore of 

 comparatively little phylogenetic value. In time, the 

 thoracic legs become fully developed and the abdominal 

 legs grow out until finally the adult stage is reached. 



The Chilopoda or Centipedes and the like are repre- 

 sented by Scolopendra (No. 943). They have a de- 

 pressed body consisting of fewer segments than are 

 found in the Diplopoda. Each apparent segment bears 

 one pair of single-clawed legs. These appendages are 

 on the sides so that they are widely separated. 



It is probable that each segment in the Chilopods was 

 originally two segments, one of which with its pair of legs 

 became atrophied. This condition is farther removed 

 from the primitive state as seen in Palaeocampa than the 

 condition of the Diplopods, and therefore the Chilopods 

 may be considered the more specialized. There is a dif- 

 ference of opinion in regard to the mouth parts of Chilo- 

 pods, some maintaining that there are three pairs and 

 others that there are four pairs. The former consider 

 that the first pair of legs are modified into poison fangs, 

 while the latter consider them as mouth organs. 



The breathing organs in the Chilopods are more spe- 

 cialized than in the Diplopods. They consist of tubes 

 which unite to form long tracheal trunks that run nearly 

 the whole length of the body. The number of spiracles 

 varies, but they generally open on alternate segments. 



The Chilopods do not leave the egg in an immature 

 condition, like the Diplopods, but this is passed within 

 the egg, and the animal when hatched is usually fully 

 formed with all the legs developed. There is accordingly 

 no metamorphosis, the development being accelerated. 



