ACTINOSPH-dERIUM EICHHORN1I. 17 



Distribution. General in the British Isles ; not un- 

 common but often local in occurrence. 



The large vacuoles forming the ectoplasm of this 

 species are very characteristic; they are so thickly 

 crowded together that they have a cellular appearance 

 and become polygonal in shape ; they increase in size 

 with the individual, the outer ones are apparently 

 empty except for a thin layer of plasma coating their 

 sides and bases, the next layers have increasingly 

 larger quantities of plasma attached to their interior 

 walls. The plasma has few inclusions and these 

 consist of food substances and undigested particles but 

 it is remarkably free from parasites and symbiotic 

 organisms; the food consists of algse, diatoms, etc., 

 and small infusoria such as ciliates, crustaceans and 

 rotifers; these active creatures fall victims to the 

 Actinosphaerium by becoming entangled among its 

 viscid pseudopodia, where they soon die and are 

 absorbed into the endoplasm (Text-fig. 181), Vogt 

 and Jung have described the formation of an amoeboid 

 pseudopodium during the process of ingestion. 



The processes of reproduction in this species have 

 been described above (p. 9), but in addition to these, 

 increase of numbers may result from what may be 

 termed mechanical division ; this usually takes place 

 if an individual becomes very large in bulk when it 

 simply separates into two or more portions ; small 

 portions artificially separated also possess the power to 

 coalesce again. 



This tendency to divide may be due to the inability 

 of large individuals to retain their normal spherical 

 form ; naturally detached portions are often 40 ^ or 

 less in diameter ; in these small individuals the large 

 vacuoles are frequently absent, the plasma presenting 

 a fairly uniform finely granular appearance. 



There are records of this species attaining to a size 

 of 1000 /x (Schaudinn) and 1360 p (Calvin) in diameter, 

 but it is very doubtful if the normal spherical sha pi- 

 is retained at over half these dimensions: 



