282 



INTRODUCTION TO CYTOLOGY 



cerned is that of the chromidia and not that of the larger nuclei, is quite 

 rare and is known as chromidiogamy . Arcella also has the other form of 

 sexual union, karyogamy. 



sh:C\ 





Fig. 111. — Copulation in Actinophrys sol. X 850. (From Minchin, after 



Schaudinn.) 



In Actinophrys sol (Schaudinn 1896) (Fig. Ill) two individuals, each 

 with a single nucleus, approach each other and become enclosed in a 

 common cyst. In each of them the nucleus now undergoes two pre- 

 liminary mitotic divisions, at each of which a small "reduction nucleus" 

 is expelled from the body in a manner very similar to the expulsion of 

 chromatin into the polar bodies of higher animals. The two individuals, 



Fig. 112. — Autogamy in Amoeba albida. (From Minchin, after Nagler.) 



or gametes, as they may now be called, fuse completely, their nuclei 

 uniting to form a synkaryon. Soon the synkaryon divides mitotically, 

 this being followed by the division of the cell to form two individuals 

 which escape from the cyst and resume the vegetative state. 



In Amoeba albida (Nagler 1909) (Fig. 112) a peculiar process known as 

 autogamy occurs while the organism is in the- encysted state. The single 



