53 



rent requisite for its full development; the naturalist 

 will often be disappointed by finding that a hard day's 

 work has not ensured him the same amount of success 

 as he would have reaped in less than half an hour in 

 many an English meadow. Do we ask, why this is so ? 

 it is impossible to reply, except on the supposition 

 that there are real physical agents, independently of 

 heat and cold, which are unfavourable in Ireland to the 

 existence of these lower creatures. We may perhaps be 

 told, by the advocates of Professor Forbes' s theory, that 

 it is the result of isolation, the quondam land of pas- 

 sage having been broken up before the proper comple- 

 ment of species had reached this large portion of their 

 western destination. But even this, although I believe 

 it to contain much presumptive truth, will not alto- 

 gether suffice to account for the phenomena which we 

 see ; for Ireland is not only remarkable for the paucity 

 of its species, but also for the paucity of its individuals, 

 and the latter fact cannot be explained by any stretch of 

 the migration-hypothesis. We are compelled therefore 

 to conclude, that Ireland, like the other countries to 

 which we have already alluded, presents conditions 

 (altogether irrespective of latitude) which must be re- 

 garded as adverse to the general prosperity of the insect 

 races. 



And so it is with localities (no less than with larger 

 countries), many of which are eminently unproductive, 

 when compared with others situated at but a short 

 distance from them. Thus, the south-western corner of 



