I. RHIZOPODA: HELIOZOA 



173 



a single (sometimes several) nucleus (w), which is vesicular, and contains 

 either one large or several smaller nucleoli. 

 A contractile vacuole is usually present. 

 Reproduction occurs by binary or multiple 

 division (fig. 120), and encystment has been 

 observed, the protoplasm dividing into many 

 hundred small amoeba;, a phenomenon always 

 connected wdth fertilization processes (au- 

 togamy?). 



Most Lobosa occur in fresh water; A. terricola 

 in moist earth. There are also parasites like A. 

 coli, rare in colder climates, frequently observed 

 in the tropics. According to recent researches 

 two forms have been included under the name 

 A. coli, one innocuous, Entamceba coli, and another 

 (possibly several) pathogenic forms, inchiding E. 

 Iiistolytica, which appears in enormous numbers 

 in abscesses of the liver and ulcers of the colon of 

 men ill with tropical dysentery For the first of 

 these it is certain, for the other probable, that 

 infection is caused by encysted forms, which arise 

 as a consequence of fertilization and are passed 

 out with the fasces. 



Fig. 120. — Amccha polypodia 

 in division (after F. E. 

 Scliulze). cv, contractile 



vacuole; el^, ectosarc; en, en- 

 tosarc; n, nucleus. 



Order III. Heliozoa, Sun Animalcules. 



The Heliozoa owe their name to the shape of the body, with the pseudopodia 

 arranged like rays. In each pseudopodium is a firm axial thread, forming a 



cv Na 



Fig. 121. — Aclinosphtrrium eichhorni. M, medullary substance witii nucleus (h); R, 

 cortical substance with contractile vacuoles {cv) ; Na, food-body. 



skeleton, and a thin coating of protoplasm. Branching and anastomoses of 

 the pseudopodia are rare. The axial threads frequently converge at the 



