RADIOLARIA 519 



wall bursts and the flagellates are liberated (g). Both isoswarmers 

 and anisoswarmers occur. The former often contain a crystal and 

 a few fat globules. Of the latter, the macroswarmers possess a nu- 

 cleus and refringent spherules in the cytoplasm. Some forms pos- 

 sess 2 flagella, one of which is coiled around the groove of the body, 

 which makes them resemble certain dinoflagellates. Further devel- 

 opment is unknown; it is supposed that the anisoswarmers are sexual 

 and isoswarmers asexual generations. Nuclear relationship (Hertwig, 

 1930). 



Enormous numbers of species of Radiolaria are known. An out- 

 line of the classification is given below, together with a few examples, 

 of the genera. 



Skeleton composed of strontium sulphate Suborder 1 Actipylea 



Skeleton composed of other substances 



Central capsule uniformly perforated, skeleton either tangential to the 

 capsule or radiating without reaching the intracapsular region. . 



Suborder 2 Peripylea (p. 520) 



Central capsule not uniformly perforated 



Capsule monaxonic, bears at one pole a perforated plate forming 



the base of an inward-directed cone 



Suborder 3 Monopylea (p. 522) 



Capsule with 3 openings: 1 astro pyle and 2 parapyles 



Suborder 4 Tripylea (p. 523) 



Suborder 1 Actipylea Hertwig 



Radial spines, 10-200, not arranged according to Midler's law. 



Spines radiate from a common center, ancestral forms (Haeckel). . . . 

 Family 1 Actineliidae 



Genus Actinelius (Fig. 219, a) 

 10-16 spines irregularly set Family 2 Acanthociasmidae 



Genus Acanthociasma (Fig. 219, b) 



Radial spines, few, arranged according to Midler's law 

 Without tangential skeletons 



Spines more or less uniform in size 



Spicules circular in cross-section Family 3 Acanthometridae 



Genus Acanthometron (Fig. 219, c) 

 Spicules cruciform in cross-section Family 4 Acanthoniidae 



Genus Acanthoma (Fig. 219, d) 

 2 opposite spines much larger Family 5 Amphilonchidae 



