52 



?iave educed applies in this case, we should expect to find 

 the eighth tentacle in each quadrant arisinf^ in a corres- 

 ponding position with relation to the interradial tentacle. 

 And such we find to be the case. Text-figure 8 sho"/s a 

 slightly older specimen of the same species, in which we 

 plainly soe the eighth tentacle in each quadrant lying in 

 its appointed place (VIII), 



It would be singular indeed if there appeared no ex- 

 ceptions at all to this regular cyclic sin-rmetry. Many va- 

 riations do occur, but not more than v/o should expect from 

 the marked tendency to variability in all parts of the me- 

 dusa. These variations no more obscure the normal definito- 

 ness of plan than the occurrences of six- or seven-rayed 

 star-fish obscure the normal pentameroi;s form in echinodenns, 

 Text-figure 5 shows an irre-^ular condition, the fourth ten- 

 tacle in each quadrant having arisen aberrantly, following 

 instead of preceding the first sense-organ (1). In figure 

 31 one of the latest arisen <iuartette has not piit in its 

 appearance (see arrow in quadrant A). In the older speci- 

 mens, the number of irregularities increases. It seems to 

 me that the bell-margin increases in extent subsequent to 

 and as a consequence of t?ie increase in the number of ten- 



