VITALITY 493 



to do with protoplasmic differeiitiations of a formative character 

 and invoh'es structures which appear for the first time, and onl\', 

 when the protoplasm is old, probably as a result of the cumulative 

 differentiation which has taken place. The sporoducts of the gre- 

 garines furnish a good illustration of this phenomenon. Here in 

 (Ircgarina cuneata, accordingly to Kuschakewitsch (1S07) the old 

 nucleus gives rise to a minute germinal nucleus while the remainder 

 is distributed as chromidia throughout the cell. The characteristic 

 sporoducts grow into the brood cavity of the sporocyst in the form 

 of tubules at the bases of which the obser^'er found collections of 

 chromidia (Fig. 121, p. 244). Similar observations have been 

 made upon other sporoduct-bearing forms (Clepsidrina, Gregarina 

 orata, etc.). These are final products of protoplasmic activity with 

 the prospective function of sporoblast elimination and have nothing 

 at all to do with fertilization (see Chapter XI). Also in the Cnido- 

 sporidia some of the residual nuclei and protoplasm become differ- 



^ 



» 



Fig. 205. — Paramecium caudaturn monster, a type common at periods of old age. 



(After Calkins.) 



entiated into sporoblast capsules while others give rise to the peculiar 

 polar capsules and the threads characteristic of these Sporozoa 

 (p. 440). 



In a number of Sarcodina, as in Gregarinida, there are special 

 morphological structures for the purpose of distributing the mature 

 j)r()ducts of multiple division. These are frequentl\' quite complex, 

 the elaters and capillitia of Mycetozoa for example, recalling the 

 spore-disseminating elements of the higher plants. The life 

 history is varied, the complications being due mainly to the forma- 

 tion of multinucleated plasmodia by fusion of numerous multi- 

 nucleated cells and to fruiting or spore structures which arise from 

 the Plasmodium. According to the later observations of Jahn 

 (1911) the Plasmodium begins as a single zygote in the form of an 

 amoeboid cell with one nucleus. This nucleus di\ides repeatedly 

 resulting in a multinucleated cell and plasmodia are formed by 

 fusion of such cells. When mature the plasmodium gives rise to 



