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. -tl). With continued 



Fig. 47 



Gametes and copulation of -Micella vulgaris. C. copula. (.\fter B^lpetiewsky). 



Fic. 48 



Stages in de\-elopment of Mastigella %-iIrea and Mastigina setosa. (.\fter Gold.schniidt. 

 X 1270. .1, flagellate stage of M. vitrea; B, same, somewhat older and before chromidia 

 formatic^n; C, same ciuring chromidia formation; a, entire cell; b, nucleus only, shinwiug 

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

 of cltroraidia; E, same, older form with pseudopodia, comi>act chromidia, and food vacuole; 

 F, same, young form witli peripheral "bristles;" G, same, formation of gametic nuclei a, 

 from iiliochromidia, b. 



o'rowth, and at maturitv of the cvcle, 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 pseudopodiospores, each with tlistributed chromatin, 

 and these form new arcella shells in which the protoplasm ultimately 



