VITALITY 279 



to be inversely proportional to the numerical importance of the 

 group. Division of the complex organization occurs in some cases, 

 e. g., Aulacantha— the nucleus dividing first, then the central 

 capsule, after which the extracapsular plasm with the skeleton 

 divides, so that each daughter cell retains one-half the skeleton and 

 regenerates the other half. In species with a firmly-knit skeleton, 

 if a special mouth opening is present, one of the daughter cells 

 emerges and builds a new skeleton (see Gromia). In some cases 

 (Thalassicollidae and Tripylea) divisions of the nuclei and central 

 capsules outrun divisions of the extracapsular plasm so that indi- 

 viduals often remain for considerable time with two, four or eight 

 central capsules recalling the permanent condition of colonial 

 Radiolaria (Collozoum, etc.). In some species, representing Spu- 

 mellaria, Acantharia and Tripylea, multiple division occurs, result- 

 ing in broods of isospores (e. g., Polycyttaria) or in some cases aniso- 

 spores which may be formed by the same parent, or by different 

 parents. Isospores are generally regarded as agametes while aniso- 

 spores are usually interpreted as macrogametes and microgametes, 

 a conclusion confirmed by Hartmann's observation of their copu- 

 lation. Chatton (1923), however, holds that, in some cases at 

 least (Polycyttaria and Collodaria), these anisospores are derived 

 from intracellular dinoflagellate parasites (genus Merodinium). 

 Both Hartmann and Belaf contend that this is a case of parallelism 

 which may indicate some phylogenetic relation between Radiolaria 

 and Dinoflagellida, for isospores, which undoubtedly are normal 

 stages in Radiolaria life histories, have Dinoflagellate characters in 

 their nuclear division figures and in their body form. Further 

 information on the life history of Radiolaria is very much needed. 



A further stage in the manifestation of differentiation at times of 

 maturity is shown by those Protozoa in which the form, character 

 and size of the fusing gametes are widely different. Here progres- 

 sive differentiation has followed two general directions resulting, 

 in one direction, in the formation of large, usually quiescent, food- 

 stored cells, the macrogametes, in the other direction, in minute 

 highly motile cells, the microgametes. In these cases furthermore 

 the differences in the gametes may be followed back through the 

 gametocytes for several generations so that cells destined to give 

 rise to macrogametes or to microgametes may be distinguished at 

 an early period. 



Examples of this type of anisogamy are practically limited to the 

 Coccidiomorpha. In the Ciliata, however, there is a partial dif- 

 ferentiation in this direction in the Vorticellidae where a larger 

 and attached individual— the macrogamete— is scarcely distinguish- 

 able from vegetative agamonts, while the microgametes are one- 

 eighth as large and are formed by three successive divisions of the 

 microgametocytes (Fig. 143). The microgametes always become 



