the resulting segments are so many gemmiparously-produced individuals, is necessarily less obvious. [Illustration: Figs. 162–165.] § 206. Evidence remains which adds very greatly to the weight of that already assigned. Thus far we have studied only the individual segmented animal; considering what may be inferred from its mode of evolution and final organization. We have now to study segmented animals in general. Comparison of different groups of them and of kinds within each group, will disclose various phases of progressive integration of the nature to be anticipated. [Illustration: Figs. 166–169.] Among the simpler _Platyhelminthes_, as in some kinds of _Planaria_, transverse fission occurs. A portion of a _Planaria_ separated by spontaneous constriction, becomes an independent individual. Sir J. G. Dalyell found that in some cases numerous fragments artificially separated, grew into perfect animals.[21] In these creatures which thus remind us of the lowest _Hydrozoa_ in their powers of agamogenetic multiplication, the individuals produced one from another do not continue connected. As the young ones laterally budded-off by the _Hydra_ separate when complete, so do the young ones longitudinally budded-off by the _Planaria_. Fig. 166 indicates this. But there are allied types which show us a more or less persistent union of homologous parts, or individuals, similarly arising by longitudinal gemmation.[22] The cestoid _Entozoa_ furnish illustrations. Without dwelling on the fact that each segment of a _Tænia_, like each separate _Planaria_, is an independent hermaphrodite; and without specifying the sundry common structural traits which add probability to the suspicion that there is some kinship between the individuals of the one order and the segments of the other; it will suffice to point out that the two types are so far allied as to demand their union under the same sub-class title. And recognizing this kinship, we see significance in the fact that in the one case the longitudinally-produced gemmæ separate as complete individuals, and in the other continue united as segments in smaller or larger numbers and for shorter or longer periods. In _Tænia echinococcus_, represented in Fig. 167, we have a species in which the number of segments thus united does not exceed four. In _Echinobothrium typus_ there are eight or ten; and in cestoids generally they are numerous.[23] A considerable hiatus occurs between this phase of integration and the next higher phase which we meet with; but it is not greater than the hiatus between the types of the _Platyhelminthes_ and the _Chætopoda_, which present the two phases. Though it is doubtful whether separation of single segments occurs among the Annelida,[24] yet very often we find strings of segments, arising by repeated longitudinal budding, which after reaching certain lengths undergo spontaneous fission: in some cases doing this so as to form two or more similar strings of segments