190 



PROTOZOA. 



quently observed in the tropics in liver abscesses and in ulcers of the 

 colon of men ill with dysentery, and perhaps the cause of the disease. 

 Some of the Monothalamia (p. 198) are sometimes referred to the Lobosa. 



Order III. Heliozoa, Sun Animalcules. 



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

 the pseudopodia arranged like rays. In the pseudopodia are a 

 firm axial thread forming a skeleton and a thin coating of 

 protoplasm. Branching and anastomoses of the pseudopodia 

 are rare, and usually occur only when the radial arrangement is 

 modified by pressure. The axial threads frequently converge at 

 the centre of the body. Here lies a granule, the centrosome 

 separated from the nucleus, which plays an important part in 

 division. The body consists of cortical and medullary portions 



No, 



cv Na 



FIG. 120. Actinosphcerium eichhorni. Jtf, medullary substance with nucleus (n) ; 

 R, cortical substance with contractile vacuoles (cv); IV, food-body. 



(fig. 120), distinguished by differences in the protoplasm, but 

 not separated by membrane. In the cortex are the contractile 

 vacuoles (cv); the medulla contains the usually single nucleus. 

 Among the polynucleate forms is the largest and one of the most 

 beautiful of fresh- water species, Actinosphcerium eichhorni. Many 



