RHIZOPODA. 



/HE whole arrangement of the beings which we are now about to examine is still 



very obscure, and the best zoologists of the present time have declared that any 



system which has been hitherto adopted can only be considered as provisional. 



«vT^^ Some writers, for example, unite the Rhizopoda with the Infusoria, while 



/*>/)?& others rank them among the Polyzoa ; and others again consider them to be 



Vv*$ c£ intermediate between the radiata and those simple forms of animal life which 



'^-2 are appropriately named Protozoa. After taking into consideration the various 



systems that have been propounded by different authors, I have come to the conclusion that, 



at all events, as a provisional arrangement, the Rhizopoda ought to be ranked as a distinct 



class, and placed in the position which they here occupy. 



The name Rhizopoda is of Greek origin, and literally signifies "root-footed." It is a very 

 appropriate title, inasmuch as they put forth certain filamentous appendages from their bodies, 

 which look very like the tender rootlets of plants, and serve a double purpose, namely, as 

 organs of progression, and as instruments whereby they may catch their prey. 



Some of these beings are quite unprotected, their soft gelatinous bodies being devoid of 

 any covering ; others are inclosed in a horny case, pierced with openings, through which the 

 filaments can be projected ; while the greater number of the known species are furnished with 

 shells very similar in form to those of the mollusks, and in some cases wonderfully similar to 

 the highly complicated dwelling of one of the highest mollusks, the pearly nautilus. 



These minute though beautiful beings exist in numbers that are only rivalled by the 

 sands of the sea for multitude ; and the vast hosts of these creatures can be barely estimated 

 even when we know that many large cities are built wholly of the dead skeletons of these 

 microscopic beings, and that in a single ounce of sand from the Caribbean Sea nearly four 

 millions of these shells have been discovered. The living species are not nearly so numerous 

 as the fossil. They can be captured in various ways. If, for example, growing alga? be 

 plucked, and placed in a glass vessel of sea-water, the Rhizopods will leave the algse, and 

 settle on the sides of the vessel. If they live in muddy substances, such as the "oyster-ooze," 

 which is especially prolific in Rhizopod forms, the upper layer of mud should be taken off and 

 stirred up in a vessel of clear sea-water, when the creatures will sink to the bottom of the 

 vessel, and may easily be separated. 



These modes are adopted for living specimens, but if the dead skeletons only are required, 

 they can be procured in many ways. One of the simplest methods of finding Rhizopod shells 

 is, to shake the dust out of sponges, and to examine it when laid thinly on black paper. An 

 ordinary pocket magnifier is employed in the search, and the shells are readily seen against 

 the black background. For removing them I always employ a single bristle, stuck into 

 a handle — one taken from a shaving-brush is, perhaps, the best adapted to the purpose — and 

 take up the shells singly by wetting the tip of the bristle. 



There is also another method whereby the empty shells may be obtained in considerable 

 numbers. The sand, mud, or other substance, in which they reside, should be well dried, 

 heated, and then stirred into water. As the chambered cells of the Rhizopods will be filled 

 with air, they will float on the surface of the water, and can be skimmed off without much 

 difficulty. 



The first sub-class of these beings is the Foraminifera, so called on account of the tiny 

 openings, or foramina, with which the pretty shells are pierced. Sometimes, however, this 



