8o 



THE INVERTEBRATA 



The pseudopodia branch, and to some extent join: they are said to 

 contain an axial filament and they show streaming of granules. The 

 central capsule is a pseudochitinous structure, of varying shape accord- 

 ing to the species, which encloses the nucleus and some cytoplasm 

 containing oil globules. It is perforated by pores, which by their 

 arrangement characterize the suborders, being evenly distributed in 

 the Peripylaea {Spume llaria), gathered into groups in the Actipylaea 

 (Acantharta), concentrated into one *'pore plate" in the Monopylaea 

 (Nassellaria), and represented by three openings or "oscula" in the 

 Tripylaea {Phaeodaria). The spicules are usually siliceous, but in one 

 group (Acantharta) they are said to be of strontium sulphate. They are 

 rarely absent, occasionally loose, but usually united into a lattice-work 



1/ V 



Fig. 67. Fossil Radiolaria. From Woods. A, Lithocampe tschernyschevi, 

 Devonian. B, Trochodisciis longispmus, Carboniferous. C, Podocyrtis schom- 

 burgki, Barbados Earth (Tertiary). A and C, Nassellaria; B, Spumellaria. 



(Figs. 67, 68), which is often very complicated, with projecting spines. 

 The latter may be radial but do not meet at a central point except in the 

 Acantharia. The outer layer of the body differs from that of the pelagic 

 Foraminifera in that the vacuoles are contained in a layer of jelly 

 (calymma) traversed by strands of protoplasm, which secrete it and 

 the vacuoles, and in that it cannot be withdrawn. 



There is no contractile vacuole. 



The Radiolaria reproduce by binary fission and by spore formation. 

 The spores found in them are sometimes alike (isospores) and some- 

 times of two kinds (anisospores) . The latter are held to be gametes, and 

 it is said that union between them has been observed. On account of 

 their resemblance to the Dinoflagellata it has been suggested that they 

 belong to parasitic members of that group. It is possible, on the other 



