class there are numerous deviations from the supposed “archetypal idea.” Still less can these traits of structure be accounted for teleologically. That certain organs of nutrition and respiration and locomotion are repeated in each segment of a dorsibranchiate annelid, may be regarded as functionally advantageous for a creature following its mode of life. But why should there be a hundred or even two hundred pairs of ovaries? This is an arrangement at variance with that physiological division of labour which every organism profits by--is a less advantageous arrangement than might have been adopted. That is to say, the hypothesis of a designed adaptation fails to explain the facts. Contrariwise, these structural traits are just such as might naturally be looked for, if these annulose forms have arisen by the integration of simpler forms. Among the various compound animals already glanced at, it is very general for the united individuals to repeat one another in all their parts--reproductive organs included. Hence if, instead of a clustered or branched integration, such as the _Cœlenterata_, _Polyzoa_ and _Tunicata_ exhibit, there occurs a longitudinal integration; we may expect that the united individuals will habitually indicate their original independence by severally bearing germ-producing or sperm-producing organs. [Illustration: Figs. 160–161.] The reasons for believing one of these creatures to be an aggregate of the third order, are greatly strengthened when we turn from the adult structure to the mode of development. Among the _Dorsibranchiata_ and _Tubicolæ_, the embryo leaves the egg in the shape of a ciliated gemmule, not much more differentiated than that of a polype. As shown in Fig. 162, it is a nearly globular mass; and its interior consists of untransformed cells. The first appreciable change is an elongation and a simultaneous commencement of segmentation. The segments multiply by a modified gemmation, which takes place from the hinder end of the penultimate segment. And considerable progress in marking out these divisions is made before the internal organization begins. Figs. 163, 164, 165, represent some of these early stages. In annelids of other orders, the embryo assumes the segmented form while still in the egg. But it does this in just the same manner as before. Indeed, the essential identity of the two modes of development is shown by the fact that the segmentation within the egg is only partially carried out: in all these types the segments continue to increase in number for some time after hatching. Now this process is as like that by which compound animals in general are formed, as the different conditions of the case permit. When new individuals are budded-out laterally, their unfolding is not hindered--there is nothing to disguise either the process or the product. But gemmæ produced one from another in the same straight line, and remaining connected, restrict one another’s developments; and that