6 THE APODIDJE PARTI 



stood, it is found to be very superficial. We shall be 

 able to show, in the following pages, that the Apodidae 

 agree in almost every detail of their organisation with 



o ^ ^5 



such an Annelid, and that any disagreement is chiefly 

 clue to further specialisation in adaptation to the 

 new manner of life described. 



Commencing with the head, we shall show how the 

 morphology of the typical Crustacean head is easily 

 explained by the bending round of the five anterior 

 segments of such an Annelid for the purpose of 

 browsing. 



The trunk of Apus will be shown to be a true link 

 between the many-segmented Annelids, and the 

 Crustacea with their small and almost constant 

 number of segments. The rise of the shield will be 

 briefly mentioned, a fuller account of it being reserved 

 till we compare Apus with the Trilobites. 



The gradual transformation of the Annelidan 

 cuticle into the exoskeleton of the Crustacea, to which 

 many of the changes in the inner organisation of the 

 latter are to be referred, will be found well illustrated 

 by the Apoclidae. 



The Annelidan parapoclia (with their dorsal and 

 ventral branches) will be shown to be capable of 

 developing every form of Crustacean limb, the reasons 

 for the suppression of one part and the development 

 of another being generally fairly evident, Apus again 

 supplying the clue. 



Coming to the inner organisation, we shall take in 

 turn, the musculature, the nervous system, the sensory 

 organs, the alimentary canal, the circulatory system, 



