76 THE OCEAN WORLD. 



salt water. Professor O. Schmidt proposes to divide it into three 

 divisions : 



1. Where the spicules assume a sex-radiate type. To this will 

 belong some of the most remarkable and beautiful of sponges, as 

 Euplectella, Aphrocallistes, Pheronema. 



2. Where the spicules are anchor-shaped, or of a pyramidal form, 

 containing many very familiar genera, especially the genus Spongilla, 

 met with in fresh water. 



3. Where the spicules are monaxial, polyaxial, or wanting. Here, 

 amid a host of genera and species, would be placed the genus 

 Spongia, to one or more species of which the various sponges pre- 

 viously alluded to as Sponges of Commerce, must b% referred. (For 

 Spongia offidnalis, see Fig. 9). 



RHIZOPODA. 



Gervais and Van Beneden include under the name of Rhizopods, 

 or root-footed animals (so called from $(& root; irofcs, iroSbs, footed 

 animals), those of the simplest organisation, which may be charac- 

 terised by the absence of a distinct digestive cavity, and by the 

 presence of diverging processes, or pseudopodia, which admit of 

 extension, and are sometimes simple, sometimes branched. These 

 pseudopodia can be completely withdrawn into the body substance 

 of the Rhizopod, and they receive their technical name from the fact 

 that they in many cases assist in the locomotion of these animals. 



The Rhizopods are found both in fresh and salt water, but 

 the marine forms are much the more numerous. The class is 

 divided into three orders, namely, the Lobosa, the Reticulosa, and 

 the Radiolaria. 



LOBOSA, OR AMCEBINA. 



In nearly all decaying animal and vegetable infusions, not quite 

 putrid, upon all oozy beds which have remained for some time 

 covered by fresh or sea water, as well as in our lakes and peat pools, 

 we find the singular beings which belong to this Order. They are 

 among the simplest organisms in creation, being reduced to but a 

 mere particle of living matter. Their bodies are formed of a gela- 

 tinous substance, without any appreciable organisation. The quantity 

 of matter which forms them is so small, that it becomes incredibly 

 diaphanous, and so transparent, that the eye, assisted by the powers 

 of the microscope, can often only take cognisance of it by a careful 

 arrangement of the light. 



