60 Introduction to Animal Morphology. 



CHAPTER IX. 



RADIOLARIA, &C. 



CLASS 6. RADIOLARIA (Mtillcr). Heteroplastic per- 

 sonse* or colonies,! with radiating, often anastomosing, 

 pseudopodia. The endosarc is enclosed in a chitinoid 

 central capsule, J pierced by fine pores, and consists of 

 fine cells, pigment, fat spheres, crystals, and protoplasm, 

 often with a median, sometimes compound, vesicle 

 (linncnblasc or vcsicula intiuia} in its centre. The pro- 

 toplasm varies from extreme fluidity (Collosphacridae) 

 to firmness (Acanthometridae). The skeleton consists 

 of spicules of silica or acanthin, lying outside, or 

 radiating and piercing through the central capsule. 

 They maybe solid, clear, or striated (as in Dorataspis), 

 or hollow, with a central canal traversed by a thread 

 of protoplasm, which projects like a flagellum. The 

 radiating spicules passing from the centre through the 

 capsule are often joined regularly or irregularly by 

 tangential beams, making up ornamental forms like 

 discs, flower baskets, c. The tangential beams may 

 exist with no radiant spicules. Within the central 

 capsule large nucleated cells sometimes exist, and 

 concretions of leucin and tyrosin (Kdllikcr}. In 

 the ectosarc there are also cellular bodies and pigment 

 spots ; and a layer of large alveolar cells often sur- 

 rounds the central capsule. Characteristic of the 



* ,w - &". t r - r. 



J Largest in Zygostcphanus, smallest in Physematium. 



Acanthin occurs in Acanthometridce, is of cartilaginous consistence, de- 

 stroyed by concentrated sulphuric acid. It seems to be the base in which 

 silica is, sometimes at least, laid down, as some acanthin spicules silicify 

 with age. 



