VITALITY 271 



grow into the brood cavity of the gametocyst in the form of tubules 

 at the bases of which the observer found collections of chromidia 

 (Fig. 125, p. 240). Similar observations have been made upon other 

 sporoduct-bearing forms (Clepsidrina, Gregarina ovata, 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 XIV). Also in the Cnidosporidia 

 some of the residual nuclei and protoplasm become differentiated 

 into sporoblast capsules while others give rise to the peculiar polar 

 capsules and the threads characteristic of these Sporozoa (p. 324). 



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

 morphological structures for the purpose of distributing the mature 

 products of multiple division. These are frequently 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 formation of 

 multinucleated plasmodia by fusion of numerous multinucleated 

 cells and to fruiting or spore structures which arise from the Plas- 

 modium. According to the later observations of Jahn (1911) the 

 Plasmodium begins as a single zygote in the form of an ameboid 

 cell with one nucleus. This nucleus divides repeatedly, resulting 

 in a multinucleated cell and plasmodia are formed by fusion of such 

 cells. When mature the plasmodium gives rise to the elaters through 

 the activity of nuclei which degenerate with the process. In some 

 forms the old plasmodium loses water, dries and forms a hard indu- 

 rated crust called a sclerotium. In the majority of forms the 

 protoplasm becomes transformed into a tough skin or membrane, 

 termed the peridium, which may be strengthened by deposits of 

 lime. Other parts of the protoplasm become modified into felted 

 spore capsules or capillitia through which the elaters ramify. 



In all of these cases of old age protoplasm the evidence justifies 

 the conclusion that the organization has become profoundly changet I , 

 the change often resulting in useful morphological and physiological 

 differentiations. The changes are of a character, however, which 

 prevents any recovery of vitality and death of the protoplasm 

 results unless gamete formation and fertilization supervene. 



(c.) Cyclical Differentiations Peculiar to Maturity.— Sexual maturity 

 in^ Protozoa is not a theory but a fact demonstrated in many dif- 

 ferent kinds of Protozoa. In many cases the young form slowly 

 grows to its adult condition; differentiations appear with continued 

 metabolism until the individual becomes a gamont and gives rise 

 to gametes. Thus in polycystid gregarines the sporozoite slowly 

 grows to its definitive size and differentiations appear with that 

 growth. The protoplasmic conditions leading to gamete formation 

 may, with equal reason, be regarded as evidence of still further 

 differentiation in the protoplasmic organization. In Schizogre- 



