462 ZOOLOGICAL GEOGRAPHY. [part in. 



all the great continents. That event certainly dates back to 

 Secondary, if not to Palaeozoic, times, because so dominant a 

 group must soon have spread over the whole continuous land- 

 area of the globe. We have no reason for believing that birds 

 were an earlier development ; and certainly cannot, with any 

 probability, place the origin of the Struthiones before that of 

 Mammals. 



Causes of the Poverty of Insect-life in New Zealand : its Influ- 

 ence on the Character of the Flora. — The extreme paucity of in- 

 sects in New Zealand, to which we have already alluded, seems 

 to call for some attempt at explanation. No other country in the 

 • world, in which the conditions are equally favourable for insect- 

 life, and which has either been connected with, or is in proximity 

 to, any of the large masses of land, presents a similar pheno- 

 menon. The only approach to it is in the Galapagos, and in 

 some of the islands of the Pacific ; and in each of these cases the 

 absence of mammals leads us to infer, that no connection with a 

 continent has ever taken place. Yet the fauna of New Zealand 

 evidently dates back to a remote geological epoch, and it seems 

 strange that an abundance of indigenous insects have not been 

 developed, especially when we consider the vast antiquity that 

 most of the orders and families, and many of the genera, of insects 

 possess (see p. 166), and that they must always have reached the 

 country in greater numbers and variety than any of the higher 

 animals. The undoubted fact that such an indigenous insect- 

 fauna has not arisen, would therefore lead us to conclude, that 

 insects find the conditions requisite for their development only in 

 the great continental masses of land, in strict adaptation to, and 

 dependance on, a varied fauna and flora of ever-increasing richness 

 and complexity. A small number of widely-separated forms, intro- 

 duced into a country where the fauna and flora are alike scanty 

 and unrelated to them, seem to have little tendency to vary 

 and branch out into that vast network of insect-life which 

 enriches all the great continents and their once connected 

 islands. 



It is a striking confirmation on a large scale, of Mr. Darwin's 

 beautiful theory — that the gay colours of flowers have mostly, or 



