54 



MANUAL OF ZOOLOGY. 



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 

 Foraminifera, from which they differ, chiefly if not entirely, in 

 the absence of a shell defending the soft sarcode of the body. 



Fig. 3. Morphology of Rhizopoda. a Amoeba, radiosa, showing the pseudopodia, 

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

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

 d Ciliated sponge-particles oiGrantia, showing the lesemblance to flagellate Infuso- 

 rians ; e Mono-ciliated sarcoid of Spongilla. (After Carter.) 



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 " contractile 

 vesicles" 



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

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

 leading points of interest in the order. The Amoeba (fig. 3, a) 

 is a microscopic animalcule which inhabits fresh water, and is 

 composed of gelatinous sarcode, which admits of a separation 

 into two distinct layers : an outer transparent layer, termed the 

 " ectosarc ; " and an inner, more fluid and mobile, molecular 

 layer, called the "endosarc." The "ectosarc" is highly ex- 

 tensile and contractile, and is the layer of which the pseudo- 

 podia are mainly composed ; whilst the " endosarc " contains 

 the only organs possessed by the animal viz., the " nucleus " 

 and " contractile vesicle " or vesicles, along with certain for- 

 tuitous cavities termed "food-vacuoles." 



It is believed by some that the ectosarc is surrounded by a 

 colourless and structureless investing membrane or cuticle; but 

 this is denied by others. Be this as it may, there is no oral 

 cavity, so far as has ever been certainly observed, and the food 

 is merely taken into the interior of the body by a process of 

 intussusception any portion of the surface being chosen for 

 this purpose, and acting as an extemporaneous mouth. When 

 the particle of food has been received into the body, the aper- 

 ture by which it was admitted again closes up, and the dis- 



