SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 345 



Secondary nuclei are formed from chromatin (chromidia) which 

 emerges from the giant nucleus into the endoplasm, the process 

 being different for different forms described, until the entire sub- 

 stance of the original nucleus is exhausted. The secondary nuclei 

 become the nuclei of flagellated swarmers. Despite the excellent 

 work of Brandt, ]VIoroff, Hartmann and Hammer, Huth, et al., the 

 reproduction of the much-studied species of Thalassicolla is still 

 incomplete, and complications described by Haecker on Oroscena 

 regalis, indicate that no common type is characteristic of the group. 



Family 1. Physematidae, Brandt.— F'orms in which the capsular 

 membrane is Aery thin, the nucleus globular and the endoplasm 

 with characteristic vacuoles. 



Family 2. ThalassicoUidse, Haeckel em. Brandt.— Forms similar 

 to the above but without intracapsular vacuoles. In both families 

 silicious spicules may be present or absent ( Thalassicolla). 



Family 3. Thalassophysidae, Brandt.— Forms similar to the above 

 but with the nucleus drawn out into peripheral pouches ( Thalasso- 

 yhysa).^ 



Family 4 Thalassothamnidse, Haecker. —Huge forms with a single 

 giant double spicule, and with globular or branched central capsule. 

 {Thalassothamnus, Haecker, Cytocladus, Schroder). 



Family 5. Orosphaeridae, Haeckel.— Forms with a thick latticed 

 .skeleton bearing radiating thorn-like and branching spines {Oroscena, 

 Haeckel). 



Order H. ACTIPYLEA, Hertwig. 



In additi(jn to the regularity in distribution of the pores of the 

 central capsule, the Actipylea or Acantharia are distinguished from 

 all other Radiolaria by the composition of the skeleton. Not only 

 does it differ in its chemical make-up (strontium sulphate) but it 

 also differs in its mode of formation and in its structure. The 

 essential elements of the skeleton are radial bars which originate in 

 the center of the central capsule and extend outward through the 

 capsule and extracapsular protoplasm. These bars, furthermore, 

 are arranged in a definite pattern which is so characteristic and 

 invariable that it has become known as the Miillerian law. With 

 a few exceptions in which the number of bars is a multiple of 20, 

 the bars are twenty in number and the geometrical arrangement 

 indicatefl by the ^Miillerian law, is such that the points of the spines 

 fall in five circles parallel with the equator, and with four spines to 

 each circle. The spines or bars, are named according to this 

 scheme: Polar, tropical, equatorial, sub-tropical and sub-polar 

 (Fig. 152). 



The spines are co\'ered with a sheath of gelatinous nature to which 

 peculiar muscular threads— termed myophrisks— are attached. 



