ZOOLOGY OF SCILLY. 243 



animals, wlio require, among other things, lime for 

 their shells. Drear and barren is many a hopeful- 

 looking reef here : and barren they would all be, were 

 it not for the compensating conditions of climate and 

 tidal current. Scilly is a little to the west of the sixth 

 degree of western longitude, and exactly in the fiftieth 

 degree of northern latitude ; consequently it is the 

 most southern part of the United Kingdom, if we 

 exclude the Channel Islands. The mean temperature 

 in summer is 58°, and in winter 45°. The prevalent 

 wind is south-west, or west-south-west. As a conse- 

 quence of this equable temperature, there are nmner- 

 ous plants growing in the open air at Tresco, in the 

 garden of Mr Smith, the lord of the isles, which at 

 Kew are to be seen only in the hothouses. The aloes 

 are magnificent : and rare plants from California and 

 New Zealand flourish in profusion. From this you 

 perceive that the climatal conditions are very favour- 

 able, and, whenever RenneFs Current permits it, the 

 southern forms of animal life are swept in by the 

 Atlantic. 



One great condition demanded by the tide-hunter is 

 wanting here. There are no caves, no gullies, no huge 

 dark fissures, few overhanging ledges and rock-jDOols. 

 It has already been noticed in these pages that dark- 

 ness and depth seem primary conditions even on a 

 good coast. Within the sheltering darkness of caves 

 and fissures, these animals, impatient of the light, are 

 to be found crowding together, and are only accident- 

 ally found elsewhere. On such a coast as this you gain 



