MORPHOLOGY AND TAXONOMY OF THE SARCODINA 441 



(4) Cannopylea, in which the membrane around the pores is drawn 

 out into funnel-like projections termed astropyles of which one is 

 the primary, the other two secondary. In these forms, furthermore, 

 the central capsule is double. Haeckel found that certain types of 

 skeleton are characteristic of the different types of membrane per- 

 foration and gave corresponding names to the four legions of 

 Hertwig, viz.: (1) Spumellaria, or practically naked forms. (2) 

 Acantharia (Fig. 182), with spicules and bars supposed to be of horn 

 or acanthin, but later shown by Butschli to be composed of stron- 

 tium sulphate. — Schewiakoff (1926) separates this group as a distinct 

 sub-class because: (a) Of the chemical make-up and arrangement 

 of the skeletal bars ; (b) of the absence of a membranous and per- 

 forated central capsule which is replaced here by a more or less 

 thin plasmatic membrane without pylea; (c) of the presence of a 

 clearly-defined hydrostatic apparatus consisting of a gelatinous 

 layer which extends to the ends of the spines and is provided with 

 elastic fibers (myophrisks). — (3) Nassellaria, with skeletons and 

 spicules of silica. (4) Phaeodaria from the presence of a pigmented 

 mass or pheodium around the opening of the primary astropyle. 



The Radiolaria are holozoic throughout, and feed upon flagel- 

 lates, diatoms, small copepods, etc. These are captured through 

 the agency of widespread pseudopodia. Nothing is known about 

 the digestive processes. Symbiotic "yellow cells" (Zooxanthellae) 

 which, with the exception of the Tripylea, are characteristic of the 

 group, may play a part in the nutritive processes. 



Reproduction is primarily by binary division which begins with 

 division of the nucleus. This is followed by division of the central 

 capsule and of the extracapsular plasm. In many cases the skeletal 

 structures are also equally divided so that daughter cells must 

 regenerate the missing halves (e. g., Aulacantha) . Or one daughter 

 cell may leave the parent house and build a new one for itself. 

 Observations, however, are scanty on such phenomena. Repeated 

 divisions of the nuclei and central capsules without accompanying 

 divisions of the extracapsular plasm lead to temporary forms with 

 2, 4 or 8 central capsules (Thalassicollidae, Tripylea) while this 

 condition is permanent in the huge colony forms (Polycyttaria). 



Multiple division leading to -the formation of minute bi-flagellated 

 swarmers is not uncommon and has been observed in Peripylea, 

 Actipylea and Tripylea. In some cases only one type— isospores— 

 is formed; in other cases what are termed microgametes are formed 

 by one individual, and macrogametes by another, a condition 

 which has led to the conclusion that such anisospores are gametes. 

 This is supported by Hartmann's observation of their fusion. On 

 the other hand, the formation of the two types in one and the 

 same individual throws some doubt on their gamete nature, (hat- 

 ton (1923) indeed regards them not as belonging to the life history 



