102 THE RADIOLARIA 



horizontally and is coiled round the body of the spore, the other 

 projects freely outwards and backwards. Consequently, as these 

 minute structures dart or vibrate, they rotate unceasingly about 

 their long axis, the whole mechanism and display recalling those 

 of certain Peridiniae. 



The further history of the iso- and heterospores is unknown. 

 Brandt's recent attempts (26) to obtain conjugation between spores 

 of the same and of different individuals have been as futile as those 

 of earlier observers. If, however, we may judge by the analogy of 

 other Protozoa, and in particular by the life -history of Tricho- 

 sphaerium (Schaudinn [42]), we may presume that the heterospores 

 are male and female gametes, and that the isospores are asexual indi- 

 viduals. But on this question, as on the further one of a suggested 

 alternation between isosporous and heterosporous generations of 

 Thalassicolla, we still lack information. 



1, central capsule of Thalassicolla nucleata, Huxley, in radial section, x 100 ; a, the 

 large nucleus (Binnenblaschen) ; 6, proteid vacuoles of the intracapsular protoplasm con- 

 taining concretions ; c, wall of the capsule (membranous shell), showing the fine radial pore- 

 canals ; d, chromatin substance of the nucleus. 2, 3, Collozoum inerme, J. Miiller, two different 

 forms of colonies, of the natural size. 4, central capsule from a colony of Collozoum inerme, 

 showing the intracapsular protoplasm and nuclei, broken up into a number of isospores, each 

 of which encloses a crystal of strontium sulphate ; c, yellow cells lying in the extracap.sular 

 protoplasm. 5, a small colony of Collozoum inerme, magnified 25 diameters ; a, alveoli 

 (vacuoles) of the extracapsular protoplasm ; b, central capsules, each containing besides proto- 

 plasm a large oil-globule. 6-13, yellow cells of various Radiolaria. 6, normal yellow cell ; 

 7, 8, division with formation of transverse septum ; 9, a modified condition according to 

 Brandt; 10, division of a yellow cell into four; 11, amoeboid condition of a yellow cell from 

 the body of a dead 'Sphaerozoon ; 12, a similar cell in process of division ; 13, a yellow cell the 

 protoplasm of which is creeping out of its cellulose envelope. 14, Heliosphaera inermis, Haeck., 

 living example, X400; a, nucleus; 6, central capsule; c, siliceous basket-work skeleton. 

 15, two isospores of Collozoum inerme, set free from such a central capsule as that drawn in 4; 

 each contains a crystal 6 and a nucleus a. 16, two heterospores of Collozoum inerme, of the 

 second kind, viz. devoid of crystals ; and of two sizes, a megaspore and a microspore. They 

 have been set free from central capsules with contents of a different appearance from that 

 drawn in 4. o, nucleus. 17, Actinomma asteracanthion, Haeck., x260 ; one of the Peripylaria. 

 Entire animal in optical section, o, nucleus ; b, wall of the central capsule ; innermost siliceous 

 shell enclosed in the nucleus ; c 1 , middle shell lying within the central capsule ; c 2 , outer shell 

 lying in the extracapsular protoplasm. Four radial siliceous spines, holding the three spherical 

 shells together, are seen. The radial fibrillation of the protoplasm and the fine extracapsular 

 pseudoppdia are to be noted. IS, Amphilonche messanensis, Haeck., x 200; one of the Acan- 

 thometrida. Entire animal as seen living. (After Lankester.) 



CHIEF MODIFICATIONS OF STRUCTURE IN THE RADIOLARIA. 



The Radiolaria may be derived from such an organism as 

 Thalassicolla by (1) fission and the formation of a colony of similar 

 or dimorphic individuals imbedded in a voluminous communal jelly 

 (Sphaerozoa or polyzoic Radiolaria) ; (2) by differentiation of the 

 openings of the central capsule from its evenly porose condition 

 (Peripylaria) to a radially segregated oligo-porose type (Acantharia), 

 to a single pore-plate at one pole of the now asymmetrical capsule 

 (Monopylaria), or to a single main aperture and two lateral ones 

 (Tripylaria) ; (3) by differentiation in the ectoplasm of skeletal 

 spicules and shells of the most diverse forms, which only in the 

 Acantharia invade the endoplasm. 



