MORE COMPLICATED LIFE CYCLES 



119 



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

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

 The normal vegetative 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 



c 



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



FIG. 48 



V -v - 



^'"--^ 



a -b 



C 



'$$':;* 



.<*'*.:..' 



* ^ * * * * - 



%m 



.;:':;' 



, . &^ 



.#$m 



W3&; 



rr'--' ' o 



a 



G 



Stages in development of Mastigella vitrea and Mastigina setusa. (After Goldschmidt. 

 X 1270. ^4, flagellate stage of M. vitrea; B, same, somewhat older and before chromidia 

 formation; C, same during chromidia formation; a, entire cell; b, nucleus only, showing 

 transfusion of chromatin to form chromidia; 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 a, 

 from idiochromidia, b. 



growth, and at maturity of the cycle, these masses become distributed 

 throughout the cell body in the form of deeply staining chromatin 

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

 into a number of pseuclopodiospores, each with distributed chromatin, 

 and these form new arcella shells in which the protoplasm ultimately 



