THE SHAPES AND SIZES OF ANIMALS 119 



ends, sides, and surfaces, such as we are familiar 

 with in the higher animals. Anterior and posterior 

 ends, right and left sides, dorsal and ventral sur- 

 faces, are terms which have no meaning in 

 reference to an Amoeba, for any part of the animal 

 may go first in locomotion, and when crawling the 

 animal moves along on whatever part of its surface 

 happens to be in contact with foreign bodies. The 

 only distinction in such an animal is between 

 inside and outside, and even this is not permanent 

 in all cases. In the higher Protozoa the body 

 presents a clear distinction between its outer or 

 superficial layer, which is clearer, firmer, and more 

 contractile ; and the inner or central part, which is 

 more fluid, less contractile, and usually less trans- 

 parent ; the former being named ectosarc, the latter 

 endosarc. In the simpler forms however as may 

 be seen in many Amoebae, this distinction between 

 ectosarc and endosarc is not a constant or 

 permanent one ; the protoplasm of the whole body 

 exhibits constant flowing movements, by which 

 parts that at one time are at the surface, at another 

 are carried into the interior : in such cases the 

 ectosarc is merely the layer of protoplasm that at 

 any one moment is at the surface ; and if this 

 differs in appearance from the more deeply placed 

 protoplasm, such difference is perhaps due to the 

 effects of contact with the water in which the 

 animal dwells, rather than to any fundamental 

 distinction in structure or composition of the pro- 

 toplasm itself. 



Even amongst the Amoeboid Protozoa it is how- 



