MORE COMPLICATED LIFE CYCLES 



119 



thalamous forms. In arcella it lias been described by Hertwig('99) 

 and Elpetiewskv ('08), and the process here may serve as a type for all. 

 The normal veo;etative cell of arcella contains two nuclei which at 

 an early period begin to secrete chromatin materials, which collect 

 in masses about the nuclear periphery (Fig. 44). With continued 



Fig. 47 



^\ 9 





Gametes and copulation of Arcella vulgaris. C, copula. (After Elpetiewsky). 



Fig. 48 



Stages in tlevelopnient of Ma.stigella vitrea and Mastigina .«etosa. (.Vfter Cold.schmidt. 

 X 1270. A, flagellate .stage of M. vitrea; B, same, .somewhat older and before chroinidia 

 formation; C, .same during diromidia formati<in; a, entire cell; /), nucleus only, showing 

 transfusion of chromatin to form chroinidia; D, young Hagella stage of M. setosa, with heap 

 of chromidia; E, same, older form with pseudopodia, compact chromidia, and food vacuole; 

 F, same, young form with peripheral "bristles;" G, same, formation of gametic nuclei o, 

 from idiochromidia, b. 



growth, and at maturity of the cycle, the.se masses become distributed 

 throughout the cell body in the form of deeply staining chromatin 

 granules (Fig. 43). When fully mature the protoplasm brealcs down 

 into a number of p,scudoj)odios{)ores,ea(Ii wiili distributed chromatin, 

 and these form new arcella shells in which the protoplasm ultimately 



