RADIOLARIA 79 



Order xv. Botryoidea. As in Spyroidea, but with the cephalis 3-4 



lobed ; lower chambers, one or several successively formed. (Families 



56-58.) 

 Order xvi. Cvrtoidea. Shell as in the preceding orders, but without 



lobing or constrictions. (Families 59-70.) Theoconus Haeck. 



(Fig. 25, B). 

 D. Phaeodaria. 



Order xvii. Phaeocystina. Skeleton or of distinct spicules ; 



capsule centric. (Families 71-73.) Aulactinium Haeck. (Fig. 26, B). 

 Order xviii. Phaeosphaeria. Skeleton a simple or latticed sphere, 



with no oral opening (pylome) ; capsule central. (Families 74-77.) 

 Order xix. Phaeogromia. Skeleton a simple latticed shell with a 



pylome at one end of the principal axis ; capsule excentric, sub-apical. 



(Families 78-82.) Pharyngella Haeck. ; Tuscarora Murr. ; Haeckel- 



iana Murr. (Fig. 28). 

 Order xx. Phaeoconchia. Shell of two valves, opening in the plane 



("frontal") of the three openings of the capsule. (Families 83-85.) 



We exclude Haeckel's Dictyochida, with a skeleton recalling 

 that of the Stephoidea, but of the impure hollow substance of the 

 Phaeodaria (p. 84). They rank now as Siliconagellates (p. 114). 



The Radiolarian is distinguished from all other Protozoa by 

 the chitinous central capsule, so that its cytoplasm is separated 

 into an outer layer, the extracapsular protoplasm (ectoplasm), 

 and a central mass, the intracapsular, containing the nucleus. 1 



The extracapsular layer forms in its substance a gelatinous 

 mass, of variable reaction, through which the plasma itself 

 ramifies as a network of threads (" sarcodictyum "), uniting at 

 the surface to constitute the foundation for the pseudopodia. 

 This gelatinous matter constitutes the " calymma." It is largely 

 vacuolated, the vacuoles (" alveoli "), of exceptional size, lying 

 in the nodes of the plasmic network, and containing a liquid 

 probably of lower specific gravity than sea water ; and they are 

 especially abundant towards the surface, where they touch and 

 become polygonal. On mechanical irritation they disappear, to 

 be formed anew after an interval, a fact that may explain the 

 sinking from the surface in disturbed water. This layer may con- 

 tain minute pigment granules, but the droplets of oil and of 

 albuminous matter frequent in the central layer are rare here. 



1 Verworn has shown that Thalassicolla nucleata can, when the exoplasm i- 

 removed from the central capsule, regenerate it completely. First a delicate exo- 

 plasm gives off numerous fine radiating pseudopodia, and the jelly is re-formed at 

 their bases, and carries them farther out from the central capsule. See General 

 Physiology (Engl. ed. 1899), p. 379. 



