GENERAL SKETCH 



55 



spore-formation or the breaking up of the body ' into many small 

 particles, each the germ of a new organism. While the major- 

 ity of the Protozoa reproduce asexually in these ways, reproduc- 

 tion in some is bound up with complete sexual differentiation, and a 

 series of forms may be selected which indicate the probable develop- 

 ment of the sexual from the more primitive methods. In numerous 

 cases the sexual phenomena include many of the preliminary matura- 

 tion stages shown by the Metazoa, in the formation of polar bodies 

 and reduction of the quantity of chromatin, etc. 



Simple division, the most common method of reproduction, is 

 usually a separation of the body into two equal parts either long'itu- 



A B C 



Fig. 23. — Division (budding) of Euglypha alveolata Duj. [SCHEWIAKOFF.] 

 The shell-plates which were stored in the endoplasm about the nucleus pass out with the stream- 

 ing protoplasm (A) to form the shell of the daughter-cell. The nucleus is shown in different stages 

 of mitosis. 



dinally (Flagellidia) or transversely (Ciliata). It is invariably preceded 

 by division of the nucleus, and is often accompanied by the equal 

 division of certain of the internal structures of the cell, such as the 

 chromatophores, pyrenoids, etc. It may take place either during 

 active life or under the protection of a cyst. Ciliata in the process of 

 division may be frequently seen swimming about actively, the con- 

 necting-strand becoming narrower and narrower, until finally only a 

 delicate strand of protoplasm separates the daughter-cells, and this, 

 after a few energetic contortions, gives way and the young cells are 



