The principles of biology . more in these than in the Sponges or thecompound Vorticellce, do we find such co-ordination as givesthe whole a Kfe predominating over the lives of its have not yet reached an aggregate of the second order,so individuated as to be capable of serving as a unit in still higher combiaations. But inthe class Ooelenterata, this ad-vance is displayed. The com-mon Hydra, habitually taken asthe type of the lowest divisionof this class, has specializedparts performing mutually-subservient functions; and thusexhibiting a total life distinct from the lives of the imit
The principles of biology . more in these than in the Sponges or thecompound Vorticellce, do we find such co-ordination as givesthe whole a Kfe predominating over the lives of its have not yet reached an aggregate of the second order,so individuated as to be capable of serving as a unit in still higher combiaations. But inthe class Ooelenterata, this ad-vance is displayed. The com-mon Hydra, habitually taken asthe type of the lowest divisionof this class, has specializedparts performing mutually-subservient functions; and thusexhibiting a total life distinct from the lives of the 146 represents one of these creatures in its contractedstate and in its expanded state; while Fig. 147 is arude diagram from memory showing the wall of thiscreatures sack-Kke body as seen in section imder themicroscope: a and h being the outer and inner cellularlayers ; while in the central space between them, isthat nucleated substance, or sarcode, or protoplasm,in which the cells originate. But this lowly-organized. THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 83 tissue of tlie Hydra, illustrates a phase of iategration inwMch the lives of the minor aggregates are only par-tially-subordinated to the life of the major aggregateformed by them. For a Hydrc^s substance is separable intoAmoeba-Vike portions, capable of moving about independ-ently. Prof. Green quotes Ecker, Lewes, and Jager, in proofthat this animal exhibits, at certain seasons of the year, atendency to break up into particles of a sarcode aspect, whichretain for a long time an independent vitality. And if webear in mind how analogous are the extreme extensibilityand contractility of a Hydras body and tentacles, to the pro-perties displayed by the sarcode among Rhizopods; we mayinfer that probably the movements and other actions of aHydra, are due to the half-independent co-operation of theAmoeba-]ikG individuals composing it. § 202. A truth which we before saw among plants, wehere see repeated among animals—
Size: 1966px × 1271px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, booksubjectbiology, bookyear1864
