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GARY N. CALKINS 



end, the other a vigorous backward leaping movement due to the 

 giant cirri. When irritated the organism gives a backward leap 

 with one or a few of the posterior cirri, moving only two or three 

 times the length of the body; this is repeated for three times as a 

 rule, and then, if the irritation continues, all of the caudal cirri 

 are brought into play and the cell is swept away backwards like 

 a flash. It darts back and forth across the watch glass for several 



Fig. 2 Stages in the normal cell division of Uronychia (camera drawings from 

 preparations). A, later stage in the condensation of the macronucleus, three 

 spheres not yet fused. The micronucleus is in the end phase of division. A new 

 cirrus is forming in the regeneration zone of the anterior organism, and new cirri 

 have replaced the old ones of the posterior end. B, C, later stages in division. 



seconds, finally coming to rest with a jerk and moving off at once 

 in the opposite direction. Its movements are strikingly sug- 

 gestive of a bird's flight and manner of alighting. 



Division. Under the cultural conditions of the laboratory, 

 Uronychia divides about once in 36 hours. The process is com- 

 plicated and after the first visible evidence of division, requires 

 about 6 to 8 hours for completion. As Wallengren ('01) showed 



