- PROTOZOA; AMCEBEA. 63 



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

 tile vesicles ." 



The ' Am<Kba\ 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. 8, B) 



Fig. 8, A, Ai 

 B, Amoeba grinceps 

 cleus ; e Ectosarc. 



developed in organic infusions (after Beale), greatly enlarged ; 

 $s (after Carter) ; v Villous region ; c Contractile vesicle ; Nu- 



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 

 aperture, 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- 

 charge of solid excreta is effected in an exactly similar manner. 



* Greeff has shown that some species of Amceba (such as A. terricola) 

 inhabit moist sand or earth. 



