RADIOLARIA. 879 



Collodaria, brown in many Spumellarian Sphaeroidea and Discoidea, red in 

 some Acantkaria. The Phaeodaria are characterised by a dark mass, the 

 phaeodium, of a greenish-brown or black hue surrounding the astropyle. It 

 consists of rounded bodies, the phaeodellae, sometimes nucleated, ranging 

 from 'oo i to -05 mm. in size, mixed with minute black particles. It is not 

 certain whether or no they belong to the organism or are symbiotic algae. 



The colonial Radiolarians, i. e. some Spumellarian Collodaria and 

 Sphaeroidea, differ from the non-colonial in possessing numbers of central 

 capsules, each with its own sarcomatrix, but with a common calymna and 

 sarcoplegma; The individuals in these colonies, when adult are usually 

 placed peripherally, whilst one or more vacuoles occupy the centre ; they 

 retreat on irritation from the surface. The colony may be spherical, 

 elongated, rarely ring-shaped. Colonies of the same species, even if in 

 different stages of growth, fuse when brought into contact, either naturally 

 or artificially ; and colonies of different species may adhere without fusion, 

 especially if the water is somewhat foul. 



Reproduction takes place by fission or spore-formation, rarely by 

 gemmation. Binary fission of the young central capsule appears to occur 

 in the colonial genera and in some tripylean Phaeodaria, i. e. those with 

 three apertures to the central capsule. It is possible that it may be 

 general. Young colonies of some species of Collozoum and Sphaerozoum 

 contain in the sarcoplegma structures known as ' extra-capsular bodies/ 

 produced by gemmation from the central capsules. They are strongly 

 refractile, non-granular, provided with differentiated nuclei and groups of 

 oil-drops. They give origin to anisospores in some instances, in others 

 probably to central capsules. In the colonial Collosphaera and its allies 

 the stage of growth in which a few individuals furnished with shells, and 

 many without them, make up the colony, is perhaps comparable (Brandt). 

 The colonies themselves are said also to multiply either by breaking at 

 their nodes, e. g. the elongated beaded adult colony of Collozoum, or by 

 simple constriction whilst young, e.g. spherical colony of Collosphaera. 

 It may be noted that a young colony, at least in some instances, contains 

 many more individuals than an adult. 



Spores have been observed in the four main sub-divisions of the class, 

 but the mode of their formation is most accurately known in the colonial 

 Collodaria. It takes place in the central capsule, the extracapsular 

 region having no share in it, unless a small portion of the sarcomatrix is 

 retracted. There are two kinds of spores, iso- and aniso-spores, which 

 differ from one another (i) in the mode of their formation, (2) in the 

 character of their nuclei, and (3) in Collozoum and Sphaerozoum by their 



Haeckel to the vacuoles of the extracapsular region. Brandt denies the existence of a special 

 membrane to the central jelly- spheres of Collosphaera, &c., said to be present by Hertwig and Haeckel : 

 see pp. 59-60 of his monograph cited p. 874, note 2. 



