it has no reference to any primordial segmentation, since the myotomes have been functionally generated. The second comment is that whereas the nephridia of the Annelid have independent external openings, the nephridia in the Elasmobranch have not. These discharge their secretions into certain general tubes of exit common to them all; showing that each of them, instead of being a member of a partially independent structure, is united with others in subordination to a general structure. That is to say, the segmentations are far from being parallel in their essential natures. The assertion accompanying these criticisms, that there is “no difference _in principle_ between the segmentation of _Amphioxus_ and Annelid” is difficult to reconcile with the visible contrast between the two. Whatever local segmentations there are in an _Amphioxus_ appear to me quite unlike “in principle” to those which an Annelid exhibits. Could its portion of gut be duly supplied with nutriment, the segment of a low Annelid could carry on its vital functions independently. In the parts of the _Amphioxus_ we see nothing approaching to this. Cut it into transverse sections and no one of them contains anything like the assemblage of structures required for living. The _Amphioxus_ is a physiological whole, and in that respect differs radically from the Annelid, each segment of which is in chief measure a physiological whole. No occurrence of local segmentation in the _Amphioxus_ can obliterate this fundamental contrast. An accompanying contrast tells the same story. On ascending from the lowest to the highest annulose types we see a progressing integration, morphological and physiological; so that whereas in a low annelid the successive parts are in large measure independent in their structures and in their lives, in a high arthropod, as a crab, most of the parts have lost their individualities and have become merged in a consolidated organism with a single life. Quite otherwise is it in the vertebrate series. Its lowest member is at the very outset a complete morphological and physiological whole, and the formation of those serial parts which some think analogous to the serial parts of an Annelid, begins at a later stage and becomes gradually pronounced. That is to say, the course of transformation is reversed.] CHAPTER VI. MORPHOLOGICAL DIFFERENTIATION IN PLANTS. § 212. While, in the course of their evolution, plants and animals have displayed progressive integrations, there have at the same time gone on progressive differentiations of the resulting aggregates, both as wholes and in their parts. These differentiations and the interpretations of them, form the second class of morphological problems.