He conceived a picture of coops and runs, outsize and still more outsize coops, and runs progressively larger.

Chicks are so accessible, so easily fed and observed, so much drier to handle and measure, that for his purpose tadpoles seemed to him now, in comparison with them, quite wild and uncontrollable beasts.

He was quite puzzled to understand why he had not thought of chicks instead of tadpoles from the beginning.
Among other things it would have saved all this trouble with his cousin Jane.

And when he suggested this to Redwood, Redwood quite agreed with him.
Redwood said that in working so much upon needlessly small animals he was convinced experimental physiologists made a great mistake.

It is exactly like making experiments in chemistry with an insufficient quantity of material; errors of observation and manipulation become disproportionately large.