SECT, ii THE OUTER BODY FORM 25 



Apodid^e are but slightly modified Annelids, the 

 widening of the head being due simply to a fold of 

 the skin ; and the cuticle being for the most part thin 

 like that of the Annelids, showing, however, localised 

 thickenings in which we can recognise the commence- 

 ment of the Crustacean exoskeleton. 



The hinder part of the body the trunk has long 

 been recognised as worm-like, but we here see that 

 the front or head part is also essentially Annelidan, 

 especially in its possession of a prostomium or upper 

 lip. The head of Apus differs from that of our 

 Annelid only in the development of the shield and 

 of the ridge-like fold which gives the head its great 

 breadth. 



The Annelid character of the Apodidae, thus visible 

 in the form of the body (i.e. of both head and trunk), 

 will be even more clearly seen when we come to 

 consider the appendages. 



