PROTOZOA: RHIZOPODA. 49 



The class Rhizopoda is divided into five orders — viz., the 

 Monera, the Ammbea, the Foraminifera, the Radiolaria, and 

 the Spongida, of which the last is occasionally considered as 

 a separate class. 



Order I. Monera. — This name has been proposed by 

 Haeckel for certain singular organisms which may provision- 

 ally be regarded as the lowest group of the Rhizopoda. They 

 are very minute in size, and are distinguished by the fact that 

 the body is composed of structureless sarcode, capable of emit- 

 ting thread-like prolongations or pseudopodia, but destitute of 

 either nucleus or contractile, vesicle. The pseudopodia are in 

 the form of delicate filamentous processes of sarcode, which 

 interlace and anastomose with one another in every direction, 

 and which exhibit a circulation of minute molecules and gran- 

 ules in their interior, and along their edges. The body, when 

 at rest, is more or less nearly circular in form, but it is capable 

 of undergoing manifold changes of figure. No hard covering 

 or " test " is ever developed. Reproduction is mostly by fis- 

 sion, with or without precedent encystation and quiescence. 

 So far as is known, all the Monera are marine, and their syste- 

 matic position is still doubtful. From the absence of a nucleus 

 and contractile vesicle, and from the nature of the pseudopodia, 

 they would appear upon the whole to be most closely allied to 

 the Foramimfera, from which they differ, chiefly if not entirely, 

 in the absence of a shell defending the soft sarcode of the 

 body. 



Fig. 2, — Morphology of Rhi/cpod'a. n Atnceia radiosaf showing the pseudopodia, 

 contractile vesicle, and nucleus ; b Dijfftugia^ with the pseudopodia protruded from 

 the anterior end of the carapace; c Individual sponge-particles, or "sarcoids ;" d 

 Ciliated sponge-part'icles of Graniijc, showing the resemblance to flagellate Infusori- 

 ans; ^Mono-ciliated sarcoid of .y^ow^-iV/a. ^ter Cairter.) 



Order II. Amcebea. — This order comprises those Rhizopoda 

 which are, with one or two exceptions, naked, have usually short, 

 blunt, lobose pseudopodia, which do not anastomose with one 

 another, and contain a "nucleus^' and one or more " contrac- 

 tile vesicles." 



The Amoeba, or Proteus-animalcule, may be taken as the 

 type, and a description of it will be sufficient to indicate the 



