1902.] NATURAL SCIENCES OF PHILADELPHIA. 777 



While I have not had a great number of specimens of the polyps 

 from which to compute averages, my counts show quite a striking 

 similarity to those which are given by Dr. Hargitt for the adults. 



Among all the varieties of geometrical figures which appear in 

 the arrangement of parts among the various orders of coelenterates, 

 there is none, so far as I can find, which is at all comparable with 

 that which appears in the arrangement of tentacles and sense- 

 organs in Gonionema. The only suggestion of such a plan of 

 arrangement as this is given in a paper on the later development of 

 Aurelia, by Friedemann (1902). In the course of the paper this 

 author describes the origin of the eight leutacles which follow the 

 first eight. Four of these appear at once, the other four later. In 

 the appearance of the first four, two possibilities arise, according to 

 Friedemann. ^Either the four arise in bilaterally symmetrical 



Fig. 12. Fig. 13. 



positions in the four quadrants, the two halves of the tentacle-ring 

 being reflected images one of the other, and the new tentacles ap- 

 pearing one on either side of the two opposite perradial tentacles 

 (fig. 12) ; or else they appear in identical positions in the four 

 quadrants, one appearing next in front of each perradial tentacle, 

 as the hands of a watch move (fig. 13). Friedemann's figures do 

 not make it clear that he actually found specimens in exactly this 

 stage. It appears more probable that he interpreted older stages 

 by this theory. But it may easily be true that in other groups 

 than that to which Gonionema belongs the tentacles originate 

 according to a plan of cyclic symmetry, or that such a condition 

 sometimes appears, irregularly, as may be the case in Aurelia. In 

 Gonionema the rule holds with remarkable constancy. 



