xi INTRODUCTION. 
the stages of their retreat away from the evolutionary centre, in avoidance 
of the competition from the improved races that have succeeded them. 
A study of the various groups attests the accuracy of this important 
generalization and law, and demonstrates that the distribution and dis- 
persal of animal life generally is not that illogical process, as some aver, 
in which the weak and strong forms of life equally multiply, increase in 
numbers and promiscuously invade each other’s territories ; but, as it 
cannot be too strongly emphasized, the distribution over the globe of all 
life is based upon the domination, greater increase, and consequent 
spreading of the stronger and most recently evolved forms, and the 
enforced retirement before them of the weaker and less adaptable species, 
which in their turn press upon and successfully compete with the still 
more primitive species that preceded them. 
This is abundantly manifest when the phenomena are impartially 
studied and it becomes clear that the representatives of weaker races are 
not advancing and never do permanently advance towards the European 
region, but in every case are retreating further and further from the 
original evolutionary region before the more powerful species originating 
there, and which as a consequence of their predominance and adaptability 
increase rapidly in numbers, and must therefore perforce extend their 
boundaries. 
Still further confirmation is given by our experience of European 
species when transferred to a new country amidst a palpably weaker fauna 
or flora, as in New Zealand; under such circumstances the intruders 
prosper amazingly to the detriment and eventual extirpation of the 
indigenous species; whilst on the contrary any attempts to permanently 
naturalize the organisms of a weak country within the European region 
are foredoomed to failure. 
The highest evolution is shown by the marvellous adaptability and pre- 
dominance of the European forms, and is internally evidenced by a greater 
concentration of the cesophageal ganglia within the cephalic region, while 
a potential ability to resist hard conditions may be conferred by the 
elaborate intestinal coiling, which gives a greater digestive and absorptive 
power, and therefore will enable the maximum nourishment to be derived 
from the most meagre amount of food. 
This predominance of the European forms of life is not confined to 
mollusks, as Prof. Alfred Newton, our most philosophical ornithologist, 
has averred that amongst the birds also, the weaker types have been very 
generally eliminated in the western paleearctic region, and that all the 
species are of the most dominant character, with the greatest powers 
of dispersal, and these features are as strongly shown by the mammals 
and other groups. 
