28 GENERAL CONSIDERATIONS 



while two new oral aggregates are provided for the daughter individ- 

 uals (Fig. 8). 



In the majority of Sporozoa and Sarcodina simple division is not the 

 usual mode of reproduction. Where it does occur, as in Amoebida, 

 characteristic derived structures are absent and, if reorganization takes 

 place, it is confined to the cytoplasm, where we have little evidence of 

 change. A modified type of division, called "budding division," is widely 

 spread in testacea. Here, water is absorbed by the old protoplasm, fol- 

 lowed by lively cyclosis and the protrusion of a protoplasmic bud from 

 the shell mouth. This bud grows, assumes the form of the parent 

 organism, and secretes its own chitinous membrane on which foreign 

 bodies (Arcellidae), or plates manufactured by the parent protoplasm 

 (Euglyphidae), are cemented. Apart from withdrawal of old pseudo- 

 podia, there is little evidence of reorganization. In Heliozoa, however, 

 pseudopodia, with their axial fiilaments, are drawn in and new ones 

 are formed by the daughter cells. 



In Radiolaria, Foraminifera, and Mycetozoa, indeed in the majority 

 of the Sarcodina and in most Sporozoa binary fission is replaced by 

 multiple division. The nuclei divide repeatedly, and a portion of the 

 cytoplasm is finally parceled out to each of the nuclei. The minute cells 

 thus formed leave the parent organism usually as swarm spores. Meta- 

 bolic products, waste matters, and certain structures of the derived 

 organization are left behind, and shells and skeletons alone mark the 

 previous existence of living cells. There is often a small amount of 

 protoplasm retained in these alloplasmatic products and it is not alto- 

 gether fantastic to see in these remains what Weismann (1880-82) 

 denied as occurring in Protozoa — viz., a corpse. 



It might seem that these methods of restoring protoplasm to its 

 full vitality by processes of division are adequate to account for indefinite 

 longevity of Protozoa. This, however, is not the case, with the possible 

 exception of the animal flagellates, in which division in some form 

 is the only means of reproduction known. In ciliates the ability to divide, 

 if other methods of reorganization are prevented, gradually weakens; 

 the interdivisional periods are gradually lengthened, and the degenera- 

 tion of the derived structures finally results. The micronucleus may 

 hypertrophy (Calkins, 1904) or disappear (Maupas, 1888), and the 



