The synthesis of fish and insect in the birds, might be illustrated equally in detail with the former; but it will be sufficient for our purpose, that as in both the former cases, the insect and the fish, so here in that of the birds, the powers are under the predominance of irritability; the sensibility being dormant in the first, awakening in the second, and awake, but still subordinate, in the third. Of this my limits confine me to a single presumptive proof, viz., the superiority in strength and courage of the female in the birds of prey. For herein, indeed, does the difference of the sexes universally consist, wherever both the forces are developed, that the female is characterised by quicker irritability, and the male by deeper sensibility. How large a stride has been now made by Nature in the progress of individuation, what ornithologist does not know? From a multitude of instances we select the most impressive, the power of sound, with the first rudiments of modulation! That all languages designate the melody of birds as singing (though according to Blumenbach man only sings, while birds do but whistle), demonstrates that it has been felt as, what indeed it is, a tentative and prophetic prelude of something yet to come. With this conjoin the power and the tendency to acquire articulation, and to imitate speech; conjoin the building instinct and the migratory, the monogamy of several species, and the pairing of almost all; and we shall have collected new instances of the usage (I dare not say law) according to which Nature lets fall, in order to resume, and steps backward the furthest, when she means to leap forwards with the greatest concentration of energy.