[82] I use these terms with quotation-marks, because I do not admit any philosophical antagonism such as they are intended to imply. [83] "Homology" is defined by lexicographers as "the doctrine of similar parts." "Homologous organs" is a term used by scientific writers to describe organs having a relation of some proportion to each other. In this particular case of the vertebral column, the different parts of the column are treated as if they were different organs, and they are said to be homologous organs in the same animal, because they bear a certain relation or ratio of proportion to each other. [84] See the discussion of how evolution works, _post_. [85] "Biology," i, p. 387. [86] The Greek philosophers, as we have seen, before Plato and Aristotle, found that their systems of causes, which did not involve the idea of power as abstracted from substance, would not account for the phenomena of nature. With all their subtilty and ingenuity, they did not reach the truth that secondary causes are necessarily limited in their action, and that there must be an unlimited cause. [87] "Biology," i, pp. 369, 370. [88] "Biology," i, p. 388. [89] "Biology," i, pp. 390, 391. [90] "Biology," i, p. 396. [91] "Biology," i, p. 399. It is to be noted that the relationship here referred to is supposed or apparent kinship between the _aggregate_ of the surviving and the _aggregate_ of the extinct forms which have died out in recent geologic times. But this does not supply the steps of descent by which any one surviving form can be traced back to any one extinct form. [92] "Biology," i, p. 401. CHAPTER VII. Mr. Spencer's agnosticism--His theory of the origin of religious beliefs--The mode in which mankind are to lose the consciousness of a personal God.