REPRODUCTION 237 



Multiple division is safely established for a number of Radiolaria 

 although it is not yet determined whether the products are agametes 

 or gametes. In many cases the flagellated swarmers which are 

 thus formed by one individual are large, while those formed from 

 another individual are smaller. This has led to the view that the 

 swarmers are anisogametes, but actual fertilization has not been 

 safely established. They are formed from the materials of the cen- 

 tral capsular protoplasm which, at first uninucleate, becomes multi- 

 nucleate by repeated divisions of the nucleus. Comparatively 

 little cytological work has been done on these forms which offer a 

 promising field for further research. According to Brandt (1885) 

 the nuclear material is distributed about the endoplasm in the 

 form of many clumps of chromatin which later become vesicular 

 nuclei and undergo mitotic divisions. Hertwig (1.879) describes 

 the nucleus of Acanthometra as composed of a large endosome and 

 a massive peripheral zone of chromatin which metamorphoses into 

 a great number of small nuclei. In Aulacantha scolymantha accord- 

 ing to Borgert (1900) the great primary nucleus gives off minute 

 chromatin vesicles until the entire substance of the original nucleus 

 is thus distributed in the endocapsular plasm and these become 

 minute nuclei which now divide by mitosis. Ultimately the central 

 capsule is dissolved, the pheodium disappears and the proto- 

 plasm breaks up into many small spheres each with several nuclei. 

 Differences in these spheres indicate the later differences in the 

 resulting swarmers. A somewhat similar history has been described 

 for the giant nucleus of Thalassicola, but despite the observations 

 of Brandt (1885), Hartmann and Hammer (1909), Huth (1913), 

 Moroff (1910) and others, the significance of the peculiar processes 

 is not clear. A rather unusual phenomenon is described by Haecker 

 (1907) in Oroscena regalis. Here the huge single nucleus of the 

 central capsule divides into two nuclei of which one remains as a 

 functional nucleus of the organism, the other is interpreted as giving 

 rise to gametocyte nuclei. There is also some evidence, not con- 

 clusive indeed, that an alternation of generations occurs, somewhat 

 as in Foraminifera. Some types give rise by multiple division to 

 isospores, c. g., Aulacantha, which are biflagellated cells with charac- 

 teristic crystalloid structures interpreted by Brandt as the product 

 of an asexual generation. Other individuals of the same species give 

 rise to broods of anisospores which are interpreted as microgametes 

 and macrogametes representing the sexual generation. 



In Mycetozoa multiple division is characteristic but complicated 

 by the typical plasmodium nature of the organisms. Such Plas- 

 modia are formed usually by the plastogamic union of amebae 

 arising from spores, the nuclei remaining separate and thus forming 

 a multinucleated protoplasmic aggregate. Many of these nuclei 

 degenerate (Kranzlin, Jahn); some become active agents in the 



