12 COLIN CLOUT'S CALENDAR. 



Tangiers, with their uniting submarine banks. Of these 

 the Spanish belt is still almost entire, and it offers no 

 special difficulty : the others are now broken up into 

 peninsulas or islands. Dr. Weismann supposes that 

 various flocks of birds grew accustomed to proceed north 

 or south along one such connecting belt, while the land 

 was still in process of subsiding : and that their descend- 

 ants still continue to follow the same lines till they 

 reach the final headlands, and then fly straight over 

 sea in a definite direction till they sight the opposite 

 land. The younger birds follow their elders : while the 

 elders themselves have learned the proper landmarks 

 and directions from similarly following their own pre- 

 decessors, and gradually take the lead in their turn as 

 the seniors drop off one by one. Thus, if we may 

 believe so plausible a theory, by a sort of unconscious 

 hereditary teaching the memory of the lost land-con- 

 nections has been handed down from one generation to 

 another since pre-glacial times. Were Corsica and 

 Sardinia now to sink slowly beneath the waves, it is not 

 difficult to conceive that the swallows might still gather 

 yearly upon the hills at Mentone, and fly southward 

 across the blank space to Tunis under guidance of their 

 most experienced elders. 



