chain of individuals arising by gemmation, and continuing permanently united end to end. Such a chain can arise only on condition that combination is more advantageous than separation; and for it to be more advantageous, the anterior members of the series must become adapted to functions facilitated by their positions, while the posterior members become adapted to functions which their positions permit. Hence, direct or indirect equilibration or both, must tend continually to establish types in which the connected individuals are more and more unlike one another, at the same time that their several individualities are more and more disguised by the integration consequent on their mutual dependence. Such being the anticipations warranted by the general laws of evolution, we have now to inquire whether there are any animals which fulfil them. Very little search suffices; for structures of the kind to be expected are abundant. In that great division of the animal kingdom at one time called _Annulosa_, but now grouped into _Annelida_ and _Arthropoda_, we find a variety of types having the looked-for characters. Let us contemplate some of them. § 205. An adult Chætopod is composed of segments which repeat one another in their details as well as in their general shapes. Dissecting one of the lower orders, such as is shown in Fig. 160, proves that the successive segments, besides having like locomotive appendages, like branchiæ, and sometimes even like pairs of eyes, also have like internal organs. Each has its enlargement of the alimentary canal; each its contractile dilatation of the great blood-vessel; each its portion of the double nervous cord, with ganglia when these exist; each its branches from the nervous and vascular trunks answering to those of its neighbours; each its similarly answering set of muscles; each its pair of openings through the body-wall; and so on throughout, even to the organs of reproduction. That is to say, every segment is in great measure a physiological whole--every segment contains most of the organs essential to individual life and multiplication: such essential organs as it does not contain, being those which its position as one in the midst of a chain, prevents it from having or needing. If we ask what is the meaning of these homologies, no adequate answer is supplied by any current hypothesis. That this “vegetative repetition” is carried out to fulfil a predetermined plan, was shown to be quite an untenable notion (§§ 133, 134). On the one hand, we found nothing satisfactory in the conception of a Creator who prescribed to himself a certain unit of composition for all creatures of a particular class, and then displayed his ingenuity in building up a great variety of forms without departing from the “archetypal idea.” On the other hand, examination made it manifest that even were such a conception worthy of being entertained, it would have to be relinquished; since in each