CHAPTER XIX 



SUBCLASS 2 ACTINOPODA CALKINS 



THE SARCODINA placed in this subclass possess axopodia and 

 are divided into two orders: the Heliozoa and the Radio- 

 laria. 



ORDER 1 HELIOZOA HAECKEL 



The Heliozoa are, as a rule, spherical in form with radiating 

 axopodia. They are somewhat similar in appearance to the 

 Radiolaria, but do not possess the central capsule of the latter. 

 The body of a typical heliozoan, such as Actinophrys, is 

 spherical when undisturbed and shows numerous radiating 

 axopodia. The cytoplasm is differentiated, distinctly in 

 Actinosphaerium, or indistinctly in other forms, into the 

 coarsely vacuolated ectoplasm and the less transparent and 

 highly vacuolated endoplasm, in which is located the nucleus. 



The food of the Heliozoa consists of living Protozoa or 

 Protophyta. Thus their mode of obtaining nourishment is 

 holozoic. A large organism may sometimes be captured by a 

 group of Heliozoa which gather around the prey. When an 

 active ciliate or a small rotifer comes in contact with an axo- 

 podium, it seems to become suddenly paralyzed and, there- 

 fore, it has been suggested that the pseudopodia contain some 

 poisonous substances. The axial filaments of the axopodia 

 disappear and the pseudopodia become enlarged and surround 

 the food completely. Then the food matter is carried into the 

 main part of the body and is digested. 



The ectoplasm contains several contractile vacuoles and 

 numerous refractile granules which are scattered throughout. 

 The endoplasm is denser and is usually devoid of granules. 

 In the axopodium, the cytoplasm undergoes streaming move- 

 ments. The hyaline and homogeneous axial filament runs 

 straight through both the ectoplasm and the endoplasm, and 

 terminates in a point just outside the nuclear membrane. 



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