S8 PROTOZOA. 



peregrinations comes across one of the microscopic algae* 

 Alimentaf e ^P°^ 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 ingestion 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 siHceous 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. Firstly, ingestion may take 

 place at any point of the surface as Amoeba has no localised 

 month or ingestive aperture, and the same remark applies to 

 egestion and the anus or egestive aperture. 



Secondly^ the food of Amoeba appears to be confined to 

 the class called proteids which are themselves constituents 

 of protoplasm. It is said that Amoeba cannot digest carbo- 

 hydrates or fats, hence it does not build up its protoplasm 

 from lower chemical constituents. Amoeba 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 

 Reproductive ^^ ^^^^ feeding and equable surroundings 

 upon an Amoeba 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 binary 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 Amoeba. 



Under unfavourable conditions, such as drought. Amoeba 

 has the power of withdrawing its pseudopodia or becoming 

 spherical. The ectoplasm secretes a thin hyaline case or 



* The food consists of diatoms, desmids, spores of algse and other 

 vegetable matters, but animal matter such as fragments of rotifers and 

 of Protozoa such as Arcella have also been observed in the endoplasm. 



