262 STUDIES, SCIENTIFIC AND SOCIAL chap. 



are apterous, but comes next to the Tenehrionides 

 vrais, of Lacordaire, which are mostly winged, 



Xenomma. — Belongs to the Aleocharides, which are 

 winged. 



Mecognathus. — Allied to Sunius, winged. 



Metopsia. — Allied to Phloeobium, winged. 



Here we have indications of an introduction of forms at 

 a still more remote epoch. In many cases the modifica- 

 tions of structure have been so great as to produce distinct 

 generic forms, while these remain still allied to winged 

 European genera. In other cases, however, the modifica- 

 tions are still greater, and the affinities are with groups 

 which in Europe are wholly apterous. Such cases as 

 Hadrus and Macrostethus, which belong to small groups 

 of wholly apterous genera, are difficulties on the theory of 

 transmission over the sea. But two considerations render 

 this difficulty less real than apparent. They all carry us 

 back to a very remote epoch ; and, knowing what we do of 

 the instability of the apterous condition, we may fairly 

 conclude that the groups in question were, at that time, in 

 a partially winged state. At or near this same remote 

 epoch, the Madeiran group, as indicated by the submarine 

 bank now connecting the several islands, probably formed 

 one more extensive island, and the distance of ocean to 

 be traversed would then have been considerably less than 

 it is now. 



If the various groups of facts which I have here set 

 forth, respecting the distribution of apterous and winged 

 species and genera, are fairly considered as a whole, I 

 think they will be seen to be quite inconsistent with the 

 theory of that distribution having been effected by a 

 former land-connection with Europe ; and, considering 

 that we are necessarily ignorant of many of the ways by 

 which organisms are transmitted across ocean barriers, 

 such transmission seems to be indicated in the case of the 

 Madeiran Coleoptera, not by means of drift wood and 

 ocean currents, which Mr. Murray thinks must be the most 

 efficient means of transport, but by some mode in which 

 their wings are called into play, which can only be by a pas- 

 sage through the air when assisted by gales and hurricanes. 



