CHROMIDIA AND NUCLEI OF A PROTOZOON 217 



empty corners of the shell, Fig. 61 : 2. At other times the 

 animal leaves its shell, 3. The chromidial reproductive 

 stages are of two kinds, non-sexual and sexual ; and the 

 sexual processes are again of two kinds, nuclear (karyogamy) 

 and chromidial (chromidiogamy). The asexual chromidial 

 reproduction is shown in Fig. 61 : 5, 6, and 7 ; really three 

 degrees of the same process. New nuclei formed from the 

 chromidium, together with the adjacent zone of cytoplasm, 

 become buds, which may be formed slowly, 5, or more 

 rapidly, 6 9 or very rapidly after the animal has left the shell all 

 but the two trophonuclei with a little plasm, 7. Karyogamy 

 is depicted in 8 and 9. Many chromidial nuclei, rather 

 larger in the female than in the male gamont, are formed, 

 and they become the nuclei of the male and female sex-cells 

 (gametes), which coalesce. 



Chromidiogamy is shown in 10 and 11. Two Arcellae, 

 after adhering by their pseudopodia, come pylome to 

 pylome, and they fuse together, nearly the whole of the 

 substance of one animal passing into the shell of the other 

 and, after mixing, returning again. The animals then 

 separate. The trophonuclei break up and new nuclei are 

 formed from the chromidium to become the nuclei of buds. 

 In whatever way buds are formed they all pass through the 

 same phases before they assume the Arcella-form. These 

 phases are shown in 12, 13, and 14 ; 13 is called the Nudearia 

 stage. 



Still another vital process common to many protozoa, 



