49 ^ Willis - — Endemic Genera of 
Age and Area with exactness in its distribution, as indicated by the right- 
angled triangle showing it gradually extending its area till at the same 
moment it reaches both north and south ends of New Zealand. Casually, 
it or some of its derivatives give rise to ten endemics (e, i to io), which 
spread in the same way. If a vertical line be drawn af each tenth of the 
total distance from north to south, and the number of endemics in each zone 
counted, they will give a curve rising to a maximum at or near the middle 
(sometimes two maxima). Here for example the figures run o, 3, 5, 8, 9, 8, 
7, 3, 2, 2. On examination, I found this maximum exhibited by every 
