194 A GENERAL VIEW OP THE 



endeavour to illustrate my remarks by refei-ence to various speci- 

 mens from the museum, 



Radiata. — Polygastrica^ Poriphera, Polypiphera, Acalepha, E- 

 chinoderma. 



Arliculala. — Entozoa, Rotifera, Cirrhopoda, Annelida, IMyriapo- 

 da, Insecta, Arachnida, Crustacea. 



MoUusca. — Tunicata, Conchifera, Gasteropoda, Pteropoda, Ce- 

 phalopoda. 



Verlchrata. — Pisces, Amphibia, Reptilia, Aves^ Mammalia. 



If we place a drop of any decayed infusion of animal or vegetable 

 matter under a powerful microscope, and pass a ray of light through 

 it, we discover in that drop various forms of living beings : some of 

 a rounded, some of a lengthened form ; others exhibiting various 

 ramifications ; but all apparently of a soft transparent texture. 

 These singular animals abound in the stagnant waters of rivers and 

 lakes, and are found in every drop of the ocean. They are called 

 Polygastrica, because, under a very high magnifying power, they 

 are observed to have several internal cavities or stomachs. Although 

 crowded together by thousands, their motions seem to be regular 

 and methodical ; and they are seen to advance, recede, and stop at 

 pleasure. 



Inhabiting the shores of the sea, covering the rocks, and some- 

 times hanging in branches from the cliffs, are the sponges and vari- 

 ous sponge-like bodies. They are termed Poriphera, from the in- 

 numerable pores, canals, and tubes, of which the firmer textures of 

 the body consist, and through which the salt-water is found con- 

 stantly circulating. When these sponges are torn from the rocks 

 the softer parts of the animal run down like oil. If at this time 

 we cut the sponge in pieces, the salt water may be seen, under the 

 microscope, rushing through the pores and canals of each separate 

 piece, although we can observe nothing in the structure to explain 

 the motion. The strongest stimuli fail in exciting the slightest 

 movement ; strong acid or a hot wire does not cause the slightest 

 trembling : yet the usual currents still go on. 



The Polypiphera inhabit the sea in every clime. These beauti- 

 ful varieties of coral and corallines now before me are the skeletons 

 of polypipherous animals, which ramify and branch out in masses 

 from the bottom of the sea. Sometimes covering these elegant 

 masses are thousands of little carnivorous animals ; sometimes in the 

 interior there is a soft fleshy substance, which is the body of the 

 animal. These polypiphera are an exceedingly interesting group, 

 well worthy your attention. 



