30 



INVERTEBRATE ANIMALS. 



Foraminifera, chiefly if not entirely, in this absence of any 

 hard covering or shell. 



ORDER II. AMCEBEA. This order is characterized by the 

 fact that the pseudopodia are mostly blunt and finger-like in 

 shape, and that the sarcode of the body contains the structures 

 known as the " nucleus " and " contractile vesicle" 



As the type of the order may be taken the Amoeba or Pro- 

 teus-animalcule, so called because of the incessant and illimit- 

 able changes of form which it exhibits (Gr. amoibos, chan- 

 ging). The Amoeba is a little microscopical creature which 

 may commonly be detected in stagnant water, especially 

 where there is decaying vegetable matter. When examined 

 under the microscope, all that would probably be seen at first 

 would be a shapeless or irregularly- spherical mass of gelati- 

 nous, jelly-like sarcode, containing scattered granules. Soon 

 the creature might be observed to push out a finger-shaped 

 prolongation of its own substance ; and it would soon be 

 found that similar processes or pseudopodia could be pushed 

 out at will from almost any point of the body and again re- 

 tracted within it without leaving any trace behind. As a 

 result of this, the form of the animal is constantly changing, 

 and hence its common name of Proteus-animalcule (Fig. 3, a). 

 By means of these temporary processes of sarcode, the Amoeba 



FIG. 3. Morphology of Ehizopoda. a Amoeba radiosa, showing the pseudopodia, the 

 contractile vesicle, nucleus, and vacuoles ; b Diffluqia, with the pseudopodia protruded 

 from the anterior end of the carapace ; c Detached sponge-particles or " sarcoids ; " 

 d Ciliated sponge-particles of Grantia; e Sponge-particle of the fresh-water sponge 

 (Spongilla) with a single cilium. 



both moves and obtains foodl Locomotion is effected in a 

 kind of creeping manner, the animal pushing out the pseu- 

 dopodia in one direction and then pulling the body in the 

 same direction. In the same way, when any minute particle 

 of food, such as a microscopic plant, comes within its reach, 

 the Amoeba wraps a pseudopodium round it, and then with- 

 drawing the pseudopodium, lodges the nutrient particle se 



