Ample materials for such experiments exist, in the numerous
"representative species" inhabiting distinct areas on a continent or
different islands of a group; or even in those found in the same area
but frequenting somewhat different stations.
To carry out these experiments with any satisfactory result, it will be
necessary to avoid the evil effects of confinement and of too close
interbreeding. If birds are experimented with, they should be allowed as
much liberty as possible, a plot of ground with trees and bushes being
enclosed with wire netting overhead so as to form a large open aviary.
The species experimented with should be obtained in considerable
numbers, and by two separate persons, each making the opposite
reciprocal cross, as explained at p. 155. In the second generation these
two stocks might be themselves crossed to prevent the evil effects of
too close interbreeding. By such experiments, carefully carried out with
different groups of animals and plants, we should obtain a body of facts
of a character now sadly wanting, and without which it is hopeless to
expect to arrive at a complete solution of this difficult problem.
Pages:
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318