PLATE 1 



EXPLANATION OF FIGURES^ 



1 to 6 Stages in the process of swallowing Paramecium caudatum. Camera 

 drawings from preparations mounted in toto. 



7 Section of dividing form of Didinium. The macronucleus section shows 

 the characteristic reticulum of the early stage of division. Two micronuclei 

 in full mitosis lie in the margin of the macronucleus; several large endoplasmic 

 bodies are shown in section, and two enigmatical bodies, which may be seizing 

 organs in the process of development. 



8. Section of Didinium preparatory to encystment. The trichites of the 

 proboscis and the basal fibrils of the membranulae are clearly shown at this 

 stage; the peripheral protoplasm is denser than at other periods; the macronu- 

 cleus shows the enlargement of the contained chromatin bodies. The micro- 

 nuclei at this stage leave the hollows in the margin of the macronucleus, swell, 

 and prepare to divide; one of the four is shown at the left of the macronucleus. 

 The seizing organ is extruded and shows the zone of dark granules near the tip. 

 These probably represent the poison of the 'trichocyst material' instrumental in 

 paralyzing the prey. 



^ Drawn by Mabel L. Hedge from permanent preparations. 



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