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The Nature of Biological Diversity 



the anterior pole. (The directions right and left will always refer to 

 the animal's right and left of the oral meridian which is considered 

 to he the midventral line.) Posterior to the mouth is a long line, the 

 cytopyge or cell anus, which lies on the postoral suture. The latter is 

 the posterior half of the oral meridian, extending from the mouth 



W0m 



•.•■•* ' S* * \Zi 





ar 



B 



v«C .•. 



_ — v * m » — 





2V "A 



-. - .....;g> p I 



FIG. 1. Photographs of P. aurelia prepared by the silver impregnation technique. 

 A. Dorsal or aboral surface. B. Ventral or oral surface. Magnification: 730 X. a, an- 

 terior pole; al, anterior left kinety field; ar, anterior right kinety field; c, cir- 

 cumoral or vestibular kinety field; cvp, contractile vacuole pore; m, mouth; 

 p, posterior pole; pi, posterior left kinety field; pr, posterior right kinety field; 

 py, cytopyge; s, preoral suture. 



posteriorly and to the left toward the posterior pole. Unlike the pre- 

 oral suture, the postoral suture is not a clear area but only a line of 

 close juncture between two different surface patterns (see below). 



Although the contractile vacuole pores and the three parts of the 

 oral meridian (preoral suture, mouth, and cytopyge) are the most 

 conspicuous features of the cortical pattern, the rest of the cortex 

 exhibits a beautiful constancy of finer patterning marked by regu- 

 larly oriented rows of dots much smaller than those representing the 



