REPRODUCTION ' 241 



little cytological work has been clone 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 (1879) 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 scaly mantJia accord- 

 ing to Borgert (1900) the great primary nucleus gives oft' 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 phfeodium disappears and the proto- 

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

 Difterences 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, e. g., Aidacantha, which are biflagellated cells with 

 characteristic 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 amoebse 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 

 formation of specialized structures of the fruiting bodies (elaters, 

 etc., Kranzlin, 1907) ; others divide by mitosis to form nuclei of the 

 spores contained with the elaters in the spaces of a meshwork formed 

 by a special protective and supporting part of the fruiting bodies 

 called the capillitium (Fig. 146, p. 328, see also p. 326). 



Multiple division in the Sporozoa is characteristic of practically 



all Coccidiomorpha, particularly in agamogony. The nuclei divide 



repeatedly by mitosis until many are formed, after which the body 



plasm breaks up into as many agametes as there are nuclei. In 



16 



