io THE APODID^ PARTI 



related to the Apodidae. Both these points will be 

 discussed more in detail in Part II. 



Finally, in a short concluding section we shall show 

 that the method of differentiation which turned the 

 Annelid into the Crustacean throws a flood of light on 

 the origin of the Tracheata, and on some of the 

 morphological differences which separate these two 

 divisions of the Arthropoda. 



Several new points in the anatomy' of Apus will be 

 described and illustrated. Where these do not bear 

 directly upon the subject, they will be given in full in 

 an appendix, so as not to interfere with the course of 

 the argument. 



