CERTAIN GENERAL CHARACTERISTICS 



35 



first an anterior region, the posterior part of the body being undeveloped 

 (Fig. 12). Development of some of these may continue posteriorly until a 

 complete individual separates from the mass (Calkins, 191 1). More re- 

 cently Sonneborn (1932) has described monsters of the ciliate Colpidium 

 campylum which appear very similar to the Paramecium monsters but re- 

 sult from culture with a strain of Micrococcus as food. Stylonychia mytilus 

 has a micronucleus and meganucleus in the anterior half of the body and 



Fig. 12. — Multiple Paramecium monsters (from Calkins, 191 1) 



another similar pair in the posterior half. In fissio. the two fields from 

 which the cirri develop are localized near each pair of nuclei. When recon- 

 stitution occurs after any injury which leaves the two pairs of nuclei in- 

 tact, the field from which the new cirri develop appears in relation to the 

 anterior pair of nuclei. Only when these nuclei are removed does a cirrus 

 field develop in relation to the posterior nuclei. The field of the marginal 

 cirri always develops in the anterior half of the body, and development 

 progresses from anterior to posterior (Dembowska, 1925). 



