[24] For the illustrations of both kinds of selection I must refer the reader to Mr. Darwin's works. In regard to birds, he makes the sexual selection operate less by the "law of battle" among the males, or by fighting, and more by the attractions of plumage and voice, by which the males carry on their rivalry for the choice of the females in pairing. But he attributes the same effect to the sexual selection in birds as in the other animals, namely, the transmission to offspring, and chiefly to the male offspring, of those peculiarities of structure which have given to the male parent the victory over his competitors. [25] A very low form of fish, without brain, vertebral column, or heart, classed by the older naturalists among the worms. ("Descent of Man," p. 159.) The technical name of the lancelet is _Amphioxus_. [26] "Origin of Species," p. 146. [27] The kangaroos and opossums are of this group. [28] Animals with four hands. [29] Animals which produce living young, and nourish them after birth by milk from the teats of the mother. [30] The lemur is one of a genus of four-handed mammals, allied to the apes, baboons, and monkeys, but with a form approaching that of quadrupeds. [31] "Descent of Man," p. 165.--The reader will need to observe that monkey is the popular name of the ape and the baboon. In zoölogy, monkey designates the animals of the genus _Simia_, which have long tails. The three classes are apes, without tails; monkeys, with long tails; baboons, with short tails. [32] Grote, iii, p. 276. [33] "Descent of Man," p. 65. [34] "Descent of Man," p. 65. CHAPTER III. The Darwinian pedigree of man--The evolution of organisms out of other organisms, according to the theory of Darwin.