854 Bibliographical Notices. 



unapproachable rock. Ha^^[ng, on the 3rd of July 1849, succeeded 

 in reaching the summit, not without much difficulty and at the 

 greatest peril (in the pursuit principally of land mollusca and plants), 

 Mr. Lowe informs me that he met with it beneath a slab of stone, 

 and that he was attracted (as already mentioned) by its remarkable, 

 stridulating noise. So local indeed does this insect seem to be, that 

 it, apparently, has not extended itself even over the Dezerta Grande 

 (where there are no external obstacles to bar its progress) ; but re- 

 tains the very position which in all probability constituted its original 

 centre of dissemination at the remote period of time when this an- 

 cient continent received its allotted forms. Judging from the slow- 

 ness with which creatures of such habits must necessarily (under any 

 circumstances) be diffiised, it is at least unlikely that the present 

 one could have circulated far, when the now submerged portions of 

 that region began to give way ; and hence it is not impossible that 

 the Southern Dezerta with the adjacent part (then united to it) of 

 the Central one may have embraced the whole area of its actual 

 primaeval range,— the remains of which (though they be now sepa- 

 rated by a channel) it still continues to occupy, and from which, even 

 where physically unimpeded, it has never roamed." 



We may also quote the following passage from p. 113 — of general 

 and great importance on the oft-mooted and much- disputed question 

 of species ; it occurs as a note to the description of Olibrus bicolor, 

 and refers to the distinctions between it and Olibrus Uquidus : — 



" There can be no doubt but that the present insect and the follow- 

 ing one approach each other very closely, and it is not without hesi- 

 tation that I have treated them as separate. For some time indeed 

 I had considered them to be but modifications of the O. bicolor ; 

 nevertheless a careful comparison of a very large series of specimens 

 has subsequently induced me to believe that they are truly distinct, 

 since there is no difficulty whatsoever in discriminating them in a 

 general way, even though it is equally certain that about two exam- 

 ples out of every forty which I have examined are doubtful, and 

 might apparently be referred to either. Still, the normal states are 

 so clearly expressed that I cannot regard these occasional liiiks as 

 more than exceptional varieties from either side, and which would 

 fall as unmistakeably into their proper spheres as any of the re- 

 mainder, were we better able to grasp their exact characteristics, and 

 to appreciate small shades of diiference which are not the less real 

 because obscure. Nor must we forget that in our ignorance of even 

 the nature of * species,' so called, we may sometimes err in attempt- 

 ing to define too rigidly the boundaries of their attributes ; for, 

 whilst, as a matter of course, we must unquestionably assume them 

 to be absolutely unconnected (that is to say, to have descended from 

 common parents, — each of their peculiar kind), yet it is difficult to 

 assert positively that creatures which in outwai'd points are thus in- 

 timately allied are of necessity so opposite in their endowments that 

 they may not now and then intermix, and produce those very aber- 

 rations (albeit perhaps not able, themselves, to perpetuate their race) 

 which we are apt to lay hold of, even when occurring thus sparingly, 



