THE ARTHROPODA iii 



Apus. After the fifth ecdysis the second antennae degenerate 

 rapidly in size and importance, and as they undergo reduction, 

 so do the provisional excretory organs which opened at their 

 liases disappear. The frontal tentacles are aborted, and the 

 paired eyes attain their ultimate structure and dimensions. 

 The first antennae acquire a joint, the limb of the mandibular 

 appendages becomes reduced to a mere palp, and after the 

 ninth ecdysis disappears altogether. The full number of 

 thoracic and abdominal limbs and appendages is gradually 

 established by continued addition of new parts behind those 

 already existing, and after the eighth ecdysis the eleventh 

 thoracic limb of the female shows signs of the differentiation 

 which leads to its being converted into the oostegopod. The 

 caudal styles increase in length, the cephalic shield extends 

 further and further backwards over the body segments, and 

 eventually, on the acquirement of all the adult characters, the 

 larva becomes a full-grown Apus. 



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