372 



THE MICROSCOPE. 



history of these minute parasites, are well worthy of 

 investigation. 



The Rhizopoda appear as creatures of a low type of 

 organization, and are considered, with the former, to hold 

 a medium state hetween animals and vegetables. Almost 

 all of tbem live in water ; it would be a fruitless search 

 to look for distinct internal organs, as the small bladder- 

 looking spaces enclosed within their substance, — believed 

 by Ehrenberg to be stomachs, — present only the appear- 

 ance of transparent gelatinous cells, or rather moving 

 spaces, within the sarcode envelope, and may be regarded 

 as the earliest dawn of a circulatory system. 



The term Rhizopoda is derived from the Greek, an<? 



i, Dijflugia proteiformis. b, Diffl-ugia oblonga. 



dentata. 



Fig. 205. — Simple Uliizopods. 



c, d, Arcella acuminata and 



means " root-footed," — the body is composed entirely of 

 gelatinous matter, sarcode, — motion being effected by the 

 extension of portions of the substance into processes, 

 which, as in fig. 205, is seen to partake of various forms. 



Lobosa. — In the deposit formed at the bottom of fresh- 

 water ponds, we may often meet with a singular minute 

 gelatinous body, which constantly changes its form even 

 under our eyes ; and moves about by means of finger-like 

 processes, called pseudopodia, which it appears to have tha 

 power of shooting out from any part of its substance. 



