438 BIOLOGY OF THE PROTOZOA 



Nutrition is holozoic, minute lobose pseudopodia being protruded 

 which capture and draw in minute organisms as food. In Campto- 

 nema, however, the axopodia are able to bend and several of them 

 may be directed toward the capture of living prey. 



Reproduction is ordinarily by binary fission or by budding, while 

 incomplete division frequently leads to colony formation as in 

 Raphidiophrys. Sexual processes have been described for only a 

 few forms (see Chapter VIII) while flagellated swarm spores, which 

 may turn out to be gametes, are known for Acanthocystis, Claihrulina 

 and Wagner ell <i. 



If doubtful forms resembling Heliozoa, but without axial filaments 

 (e. g., Nuclearia, Vampyrella, etc.), are transferred to the Rhizopoda 

 with which they have most affinities, then the classification of the 

 Heliozoa is simple. The division into orders following Hertwig 

 and Lesser (1874) is based upon the absence or upon the nature 

 of the skeleton elements. 



Sub-class II. RADIOLARIA Haeckel. 



Broadly stated the Radiolaria are pelagic organisms of the same 

 general type as the Heliozoa but offer many variations from the 

 homaxonic symmetry of the latter. They arc exclusively salt 

 water forms, surface-dwelling for the most part, but may be found 

 at great depths of the sea. Pseudo-alveoli are greatly elaborated 

 and form foam-like spheres with radiating axopodia or with soft 

 protoplasmic pseudopodia-like myxopodia, while complex skeletal 

 elements of silica or strontium sulphate afford the greatest variety 

 of structures and designs. 



A typical radiolarian may be conceived by imagining a resistant 

 membrane of organic substance, presumably chitin or pseudo- 

 chitin, between the zones of ectoplasm and endoplasm of a heliozoon 

 like Actinosphaerium. Such a membrane is present in Radiolaria and 

 is called the " central capsule" (Fig. 181). It separates the intracap- 

 sular protoplasm (endoplasm) from the extracapsular protoplasm 

 (ectoplasm). Minute openings, the pylea, through which communi- 

 cation between the two main zones of protoplasm is possible, are 

 uniformly distributed, or arranged in lines and patterns, or limited 

 in number at definite polar positions. These serve as a basis of 

 classification for the main subdivisions of the group according to 

 the scheme early adopted by Hertwig. 



The intracapsular protoplasm contains nuclei, fat particles and 

 plastids of one kind or another, and as Verworn showed, it can live 

 independently of the ectoplasm for a time but ultimately regener- 

 ates it. The outer or extracapsular plasm is composed of four parts 

 according to Haeckel. The outermost part is a zone of pseudopodia 

 which originate, however, in the more deeply lying fourth zone and 



