SEA-URCHINS AND MEDUSA. 489 



to me unexpected relations between the sea- 

 urchin and the medusa. No one suspects, I 

 fancy, at this moment, that the solid envelope 

 of the Scutellse and the Clypeasters is trav- 

 ersed by a net-work of radiating tubes, corre- 

 sponding to those of the medusae, so well pre- 

 sented by Ehrenberg in Aurelia aurita. If 

 the Berlin zoologists will take the trouble to 

 file off the surface of the test of an Echina- 

 rachnius parma, they will find a circular canal 

 as large and as continuous as that of the me- 

 dusae. The aquiferous tubes specified above 

 open into this canal. But the same thing 

 may be found under various modifications in 

 other genera of the family. Since I have 

 succeeded in injecting colored liquid into the 

 beroids, for instance, and keeping them alive 

 with it circulating in their transparent mass, 

 I am able to show the identity of their zones 

 of locomotive fringes (combs), from which 

 they take their name of Ctenophorse, with 

 the ambulacral (locomotive) apparatus of the 

 echinoderms. Furnished with these facts, it 

 is not difficult to recognize true beroidal forms 

 in the embryos of sea-urchins and star-fishes, 

 published by Muller in his beautiful plates, 

 and thus to trace the medusoid origin of the 

 echinoderms, as the polypoid origin of the 



