254 



THE PROTOZOA 



divides by a mitosis remarkable for the vast number of chromo- 

 somes, of which there may be over a thousand, and the apparent 

 absence of a centrosome. The more usual method of reproduction, 

 however, is formation of flagellated swarm-spores by a process of 

 rapid multiple fission within the central capsule. Two kinds of 

 swarm-spores are produced, which are known respectively as 

 " isospores " and " anisospores." The isospores (Fig. 108, A), which 

 are probably agametes, are all similar in size and appearance, and 

 frequently contain a crystal in their protoplasm, and are hence 

 sometimes termed " crystal-spores." The anisospores (Fig. 108, 



cc 



FIG. 107. Actinomma asteracanthion : semi-diagrammatic to show the mode of 

 growth of the skeleton. S. 1 , S. 2 , S. 3 , Three concentric lattice-work shells, 

 connected by sp., radial bars which are prolonged beyond the outermost shell 

 as spikes ; N., nucleus ; c.r ., central capsule ; ps., pseudopodia. After Biitschli, 

 Leuekart and Nitsche's " Zoologische Wandtafeln." 



B, C), probably gametes, are of two kinds, smaller microspores and 

 larger macrospores ; they differ in structure from the isospores, and 

 lack the characteristic crystal. The swarm-spores vary in struc- 

 ture in different species, but usually have two nagella. Isospores 

 and anisospores are formed in different individuals, but it is still a 

 moot point whether an alternation of generations occurs. Micro - 

 spores and macrospores may be formed in the same individual in 

 some species ; in others they are produced by different individuals. 

 Previous to formation of the swarm-spores the extracapsular region 

 of the body disintegrates, and the central capsule with its contents 



