ZOOLOGICAL GEOGRAPHY. 
[PART III. 
402 
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 belieying 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 im- 
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. l|>6), 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 
