NEMATONEURA —Animals possessed both of nerves and muscles, either without percep tible ganglionic centres of innervation, or where these do exist, they are extremely rudimentary, and not arranged in any parallel series. This division will include Ccelelmintha, Bryozoa, Rotifera, Epizoa, Echinodermata.
The term Agastrica is here proposed to in clude those lowest forms of animal existence which obviously form the transition from the Vegetable to the Animal Kingdom ; many of them indeed seeming rather to belong to the former than to the latter division of the orga nized world. Such are, for example, the con fervoid animalcules, which, in their structure arid mode of reproduction, are evidently nearly allied to vegetables, although from the seem ingly spontaneous movements of which some, the Oscillatoria', &c. are capable, they have been claimed by Zoologists as belonging to their de partment. The Sponges ( Porifera, Grant) are equally allied to vegetables in the nature of the living parenchyma that invests and forms their porous or reticulated skeletons; and most inti mately related to these,notwithstanding the diffe rent texture of their framework, are many of the lithophytous Corallincs and Fungier, the solid portions of their skeleton being in like manner deposited in an organized soft tissue, theanimal nature of which is by no means as yet clearly esta blished. All the above plant-like forms agree, however, in one grand and striking circum stance,—they are devoid of any stomachal or digestive cavity, a feature of their economy which of itself would be sufficient to raise a doubt whether they are strictly entitled to he regarded as animals or classed with the vegeta ble creation.
We need scarcely say that in the Agastrien no muscular system whatever can be detected, the living portions of their bodies being entirely made up of a soft granular parenchyma which only dubiously exhibits contractile movements under any circumstances.
In the Paypiphera we find a very extensive group of animals naturally allied to each other in the general details of their economy, but offering very great diversity of structure and external form. In the simplest or gelatinous
Polyps ( Hydride) the acrite condition of the nervous and muscular tissues is most conspicu ously exemplified. Examined under the mi croscope, the entire substance of the minute gelatinous bag composing the body of the hydra seems to consist of a glairy material, wherein are suspended coloured globules that constantly change their relative positions, and move about from place to place as the creature contracts, or extends different parts of its sub stance, but not a fibre or filament is discernible passing in any direction, nevertheless the move merits of the Hydra appear to be performed with facility, and its powers of locomotion are considerable.
In the Akyonidee and other compound cor tical Polyps, muscles of any kind are equally invisible, and the contractions observable either in the substance of the common body or in the numerous hydriform mouths that minister to the support of the general mass, seem to be entirely due to the approximation of molecules diffused through the entire substance of the animal, rather than dependent upon any thing like muscular structure ; nevertheless it has been stated, though perhaps erroneously, that some families (the Pennotulide) are able to swim from place to place by consentaneous move ments of the polyps and polyp-bearing arms with which many species are provided.
The tubular Polyps are equally devoid of any thing like muscular fibre, nevertheless the soft and uncalcified membrane that connects the Polyps to the cells wherein they are lodged, and the Bydriform Polyps themselves, are en dowed with the capability of performing all the movements required to protrude the flower-like bodies from the cups that contain them, and to seize and swallow the materials required for their support.