§ 208. Insects, Arachnids, Crustaceans, and Myriapods, are all members of that higher division of the _Annulosa_[26] called _Articulata_ or now more generally _Arthropoda_. Though in these creatures the formation of segments may be interpreted as a disguised gemmation; and though, in some of them, the number of segments increases by this modified budding after leaving the egg, as it does among the Annelids; yet the process is not nearly so dominant: the segments are usually much less numerous than we find them in the types last considered. In most cases, too, the segments are in a greater degree differentiated one from another, at the same time that they are severally more differentiated within themselves. Nor is there any instance of spontaneous fission taking place in the series of segments composing an articulate animal. On the contrary, the integration, always great enough permanently to unite the segments, is frequently carried so far as to hide very completely the individualities of some or many of them; and occasionally, as among the Acari, the consolidation, or the arrest of segmentation, is so decided as to leave scarcely a trace of the articulate structure: the type being in these cases indicated chiefly by the presence of those characteristically-formed limbs, which give the alternative name _Arthropoda_ to all the higher _Annulosa_. Omitting the parasitic orders, which, as in other cases, are aberrant members of their sub-kingdom, comparisons between the different orders prove that the higher are strongly distinguished from the lower, by the much greater degree in which the individuality of the tertiary aggregate dominates over the individualities of those secondary aggregates called segments or “somites,” of which it is composed. The successive Figs. 170–176, representing (without their limbs) a Julus, a Scolopendra, an isopodous Crustacean, and four kinds of decapodous Crustaceans, ending with a Crab, will convey at a glance an idea of the way in which that greater size and heterogeneity reached by the higher types, is accompanied by an integration which, in the extreme cases, nearly obliterates all traces of composite structure. In the Crab the posterior segments, usually folded underneath the shell, alone preserve their primitive distinctness. So completely confluent are the rest, that it seems absurd to say that a Crab’s carapace is composed of as many segments as there are pairs of limbs, foot-jaws, and antennæ attached to it; and were it not that during early stages of the Crab’s development the segmentation is faintly marked, the assertion might be considered illegitimate. [Illustration: Figs. 170–176.]