88 PROTOZOA. 
peregrinations comes across one of the microscopic algse* 
upon which it feeds, the protoplasm flows 
round the alga which passes through the 
ectoplasm into the endoplasm, the former closing up 
behind it. This is the process of zugestion of food, and 
with the alga is usually ingested a small drop of water 
which constitutes the food-vacuole. In the endoplasm the 
food is slowly digested ; its insoluble proteids are converted 
into soluble and diffusible proteids which then pass into 
the substance of the endoplasm, The cellulose walls of 
the alga and the siliceous coats of some are not digestible, 
and they are extruded or egested by the inverse process by 
which they were ingested. 
Two points are important. /7rs¢/y, ingestion may take 
place at any point of the surface as Amba has no localised 
mouth or ingestive aperture, and the same remark applies to 
egestion and the azws or egestive aperture. ‘ 
Secondly, the food of Ameba appears to be confined to 
the class called proteids which are themselves constituents 
of protoplasm. It is said that Amedba cannot digest carbo- 
hydrates or fats, hence it does not build up its protoplasm 
from lower chemical constituents. Ameba cannot live 
without free access to oxygen and it exhales carbonic acid. 
As there is no definite respiratory organ the whole surface 
of the animal must act in this capacity. The visible effect 
of good feeding and equable surroundings 
upon an Ameba is an increase in bulk—it 
grows. When a certain size is attained, the nucleus 
divides in two and then the protoplasm. Two equal-sized 
individuals are produced from the one by Jd:nary fission 
or splitting into two. The parent individual ends its life 
at the moment of reproduction in giving rise to two fresh 
individuals. 
The process of conjugation (page 39) is said to take place 
but it has not been fully followed in Ameéba. 
Under unfavourable conditions, such as drought, Ameba 
has the power of withdrawing its pseudopodia or becoming 
spherical. The ectoplasm secretes a thin hyaline case or 
Alimentative. 
Reproductive. 
* The food consists of diatoms, desmids, spores of alge and other 
vegetable matters, but animal matter such as fragments of rotifers and 
of Protozoa such as Avcella have also been observed in the endoplasm. 
