INTRODUCTORY REMARKS. x 



process of annihilation is extremely slow ; yet year after year sees 

 portions of the rocky declivities brought into rude cultivation, whilst 

 the constant search which is made after the dead plants for fuel still 

 further operates to direct the axe of the destroyer. Here then we 

 have an unmistakeable fact, and one over which it is worth while to 

 pause, not of a single species, but of a whole fauna surely dying 

 out before circumstances which are adverse to its continuance. 

 Already upwards of 50 members have been ascertained to inhabit 

 the Euphorbias ; and (as I recently mentioned) some of them lite- 

 rally swarm, to an extent which is well nigh incredible. Yet in vain 

 do we look around for anything like an adaptation to altered, and 

 ever altering, conditions ; and I will indeed venture to affirm that 

 no one instance can be produced, throughout this noble fauna, in 

 which the slightest tendency is shown by even a single species, to 

 accommodate itself to the change of circumstances, and to become 

 modified accordingly. In Lanzarote and Fuerteventura the E. .cana- 

 riensis seems to have already gone ; and what is the consequence ? 

 Simply that not one of the numerous species which characterize that 

 plant appears to have adapted itself even to the other EupliorUas ! 

 And if this be the case, Can we wonder that the extinction of the 

 latter should result in the complete disappearance, and for ever, of 

 their entire fauna ? I do not adduce this as any anomalous effect of 

 the gradual change which has long been going on in the vegetation 

 of these Atlantic Groups ; for it is precisely what I should have 

 anticipated, and in perfect accordance with what we cannot but 

 observe equally in the case of the great laurel-fauna which is 

 slowly becoming exterminated, leaving no trace behind it of its 

 many, and very peculiar, forms. 



Yet, whilst the majority of the species appear unable to survive 

 the loss (however gradual) of the particular kind of vegetation on 

 which they were originally destined to subsist, there is some reason 

 for suspecting that a considerable number may nevertheless have 

 braved many a physical change in the extent and altitude of the 

 several areas over which they had spread. For if catastrophes are 

 admitted to have had any place at all in the geological record, it is 

 clear that some result must have been afterwards traceable in the 

 regions which were disturbed and if in the regions themselves, 

 also in the economy of their occupants. Yet, provided that insta- 

 bility (to a greater or less degree) is an element in every organism, 

 it seems impossible to realize events such as those to which I now 

 allude without being struck with the conviction tliat some slight 



