PLATE 1 



EXPLANATION OF FIGURES 



The microphotographs were taken from permanent preparations stained with 

 Delafield's hematoxylin and counterstained (unless otherwise Specified) with 

 tetra-brom-fluorescic acid. The same magnification (525 diameters) was used in 

 all cases. 



15 A twin in fission (somewhat flattened). The peristomial membranelles of 

 three of the components are visible, those of the fourth are out of focus. Macro- 

 nuclei show typical structure. (Del. hem. only.) 



16 A typical twin. Side view. 



17 to 21 These figures illustrate the process of separation of a twin to form a 

 single animal. In figure 17 a twin is shown with slightly greater separation 

 anteriorly than usual. Figure 18 shows a twin, similar to that shown in figure 17, 

 in fission. The macronuclei here are somewhat fragmented. Figure 19 shows a 

 later stage in the process of separation (ventral view). Both components are, 

 during this stage, able to creep on the substratum. (Del. hem. and eosin.) 

 Figure 20 illustrates the pulling out of a cytoplasmic strand from the posterior 

 dorsal surfaces of each component. Figure 21 shows a single animal with the 

 dorsal spine resulting fron the breaking of the cytoplasmic connection in a 

 separating twin. 



22 A twin showing clearly the fusion of the posterior macronuclei of each 

 component. The anterior macronuclei are also fused, but are slightly out of 

 focus. 



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