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we might have expected, a priori, that this state, from 

 its peculiarity to the Dezerta Grande, would not only 

 have reduced in dimensions (which, it is), hut in colour 

 also (which it is not). Here, therefore, observation, in 

 situ, becomes extremely important; since such does at 

 once convince us that its almost exclusive attachment to 

 the interior of the stalks of the Silybum Marianum, 

 Grtn. (the Holy Thistle of the ancients), with which the 

 more protected portions of that island everywhere 

 abound, affords it ample conditions, even on so bleak a 

 rock, for its completion. Nevertheless, its stature (as 

 already stated) is slightly diminished in spite of this : 

 and when we come to examine the individuals which 

 infest the lichen of more open situations (aberrant how- 

 ever on the Dezerta Grande, and answering to the var. y. 

 of the diagnosis), we immediately perceive that both of 

 our required results are indicated, the reduction not 

 being limited to size, but extended also to hue. In 

 Porto Santo this modification is the normal one, where 

 the insect likewise displays the same lichenophagous 

 tendency, and where the districts in which it exists are 

 equally barren. But, if its maximum be attained in 

 Madeira proper, and a certain number of minor devia- 

 tions range throughout Porto Santo and the Dezerta 

 Grande, it still remains for us to show where its minimum 

 is to be obtained : which, true to the modus operandi by 

 which we have conjectured its divers degrees of abortion 

 to have been brought about, would seem to be centred 

 on the Northern Dezerta, or Ilhco Chao. When we bear 



