48 



is at all comparable with that which appears in the arrange- 

 ment of tentacles and sense-organs in Gonionema, The only 

 suggestion of siich a plan or arrangement as this is given 

 in a paper on the later development in Aiirelia , by Friede- 

 mann (1902). In the course of the paper the author de- 

 scribes the origin of the eight tentacles which follow the 

 original eight. Four of these appear at once, the other 

 four later. In the ajjpearance of the fii-st four, two pos- 

 sibilities arise, according to Friedmann. Either the four 

 arise in bilaterally symmetrical positions in the foiir 

 quadrants, the two halves of the tentacle ring being re- 

 flected images one of the other, and the new tentacles ap- 

 pearing one on either side of two opposite perradial tenta- 

 cles (text-figure 1); or else they appear in identical po- 

 sitions in the four qiiadrants, one appearing next in front 

 of each perradial tentacle, as the hands of a watch move 

 (text-figure 2). Friedmann' s figures do not make it clear 

 that he actually found specimens in exactly this state. It 

 appears moi'o probable from his descriptions that he inter- 

 preted older stages by this theory. But it may easily be 

 true that in other groups than that to which Gonionema be- 

 longs the tentacles originate according to a plan of cyclic 



