THE RADIOLARIA 119 



numbers and cyclical arrangement, and they resemble the peculiar 

 pseudopodia of such Heliozoa as Acanthocystis in all points except 

 in not arising from a centrosome. The peculiar cytoplasmic 

 threads that compose the so-called flagellum of the Discoidea are 

 also in all probability of a similar nature. This flagellum consists 

 of immobile pseudopodia fused into a tapering mass which projects 

 freely at one point of the ectoplasm, and its component pseudo- 

 podia, unlike those of the surrounding calymma, can be traced 

 almost to the centre of the endoplasm. They appear to spring 

 from the nucleus. 



A peculiar accumulation occurs in the extracapsulum of the 

 Tripylaria, to which the name phaeodium is given. It consists of a 

 greenish or brownish mass concentrated about the main aperture of 

 the central capsule, but extends around the capsule for a third of 

 its extent. So constant and characteristic is this coloured mass 

 that the term Phaeodaria is frequently used as an alternative to 

 Tripylaria. 



The constituents of the phaeodium in Aulacantha are various 

 partly extrinsic, partly intrinsic. To the former class belong 

 diatoms and the debris of other vegetal organisms, small Radiolaria, 

 and Crustacea. Most of these undoubtedly represent food material ; 

 the diatoms, however, may be symbiotic. The characteristic 

 elements of the phaeodium are, however, the phaeodellae, which 

 consist of spherical or ellipsoidal corpuscles which vary from less 

 than 1 (j, to 20 p, in diameter. These corpuscles occur singly or in 

 masses. They appear homogeneous, granular, or striated, and vary 

 in colour from a hyaline transparency through yellow-brown, light 

 and dark green, to black. They may be free from inclusions or 

 contain both blackish particles of varying size and refractive 

 granular spheres and rods. Towards reagents they show great 

 refractoriness, and do not give a uric acid reaction (Borgert). 



About the nature of these phaeodellae, opinion has long been 

 divided. Haeckel maintained that they were symbiotic algae, 

 other zoologists that they were food particles. The recent 

 researches of Borgert on Aulacantha have suggested another 

 explanation. Borgert has pointed out the resemblance of certain 

 granules formed in the endoplasm in the neighbourhood of the 

 astropyle to these phaeodellae, and he regards these corpuscles as 

 excretory products of the endoplasm that pass out through the 

 capsule and accumulate in the surrounding ectoplasm. Recent 

 work on the brilliantly coloured algoid structures in bathybial 

 Challengeridae and Concharidae have shown that probably both 

 assimilation and excretion are carried on in the phaeodium (36). . 



Endoplasm. The endoplasm is the site of storage and of 

 reproductive changes. It consists of a granular streaming 

 cytoplasm often highly vacuolated, and stratified radially and 



