119 



haps be pardoned if I digress so far from my immediate 

 subject as to trace out some of the actual results of iso- 

 lation in the diffusion of the Insecta (especially recogni- 

 zable in the stoppage of a former migratory progress) in 

 a few of the northern Atlantic groups. I should pre- 

 mise, however, that it is from the Coleoptera alone that 

 I shaU. attempt to draw my inferences; nevertheless, 

 since that order is more extensive than any of the others, 

 and has moreover been closely investigated in most of 

 those islands, it may possibly afford us data of sufficient 

 comprehensiveness and accuracy for practical purposes. 



To commence, then, with the Madeiras and Canaries ; 

 the first facts which isolation discloses to us, concerning 

 the statistics of a region which was once continuous 

 throughout that portion of the Atlantic, are the slowness 

 and the direction of the ancient migratory movements. 

 The former of these is rendered evident from the vast 

 number of endemic species which are at present con- 

 tained, not merely in the two groups combined, but in 

 the several islands of which each of them is composed. 

 True it is, that these peculiar forms are, most of them, 

 apterous, and of naturally sluggish self-disseminating 

 powers ; yet, still the circumstance remains, that these 

 various creatures had not overrun areas of any extent 

 before the land of passage was destroyed, — for otherwise 

 they must have occurred, now, on islands and rocks but 

 slightly removed from each other, which they do not. 

 The latter of the above conclusions, namely, the direction 

 of the migratory current, wiU become apparent in the 



