6 4 



ABSTRACTS OF PAPERS. 



[VOL. II. 



hands of a watch ; IV follows II, and the two pairs of sense 

 organs, i and 2, lie as if the cells that were to form them 

 had been crowded along to the right by the newly formed 

 tentacles. 



In an older specimen (Fig. 2) the successive pairs of tenta- 

 cles and sense organs have arisen in corresponding positions, 

 as is indicated by the numbers on the diagram. The origin 



FIG. 



of tentacles and sense organs would seem then to be governed 

 by an attempt at radial symmetry which is constantly inter- 

 fered with by this sequence of formation from left to right, 

 along the bell-margin. 



In full-grown medusae there appears a striking conformity 

 to this rule, with fewer exceptions than would be expected 

 from the frequency of other variations in all parts of the 

 creature. 



