1908.] NATURAL SCIENCES OF PHILADELPHIA. 147 



have the fullest data. Many other less common species arrived on the 

 various " wave-days," but their inclusion in the tables would only 

 tend to confusion and would obscure the point that I wish to demon- 

 strate. Where a species has been omitted in any year it is because 

 it failed to arrive on one of the wave movements, or because the bulk 

 movement was scattered and not concentrated on a "wave-day." The 

 scarcity of such omissions, however, illustrates to what an extent the 

 migration is concentrated on a comparatively small number of daj^s. 



"First arrival" in these tables denotes the first individual to be 

 reported anywhere within the ten-mile circle. 



