440 LOUIS AGASSIZ. 



both on account of their contact with the sea 

 and of the vast stretches of flat country over 

 which they extend. 



For the last few days I have been especially 

 occupied with the development of the medu- 

 sae. In studying the actiniae I have made 

 a striking discovery, and I should be glad 

 if you would communicate it to the Acad- 

 emy in advance of the illustrated paper on the 

 same subject, which I hope soon to send you. 

 Notwithstanding their star-like appearance, 

 the star-fishes have, like the sea-urchins, in- 

 dications by no means doubtful, of a symmet- 

 rical disposition of their organs in pairs, and 

 an anterior and posterior extremity easily rec- 

 ognized by the special form of their oral 

 opening. I have now satisfied myself that 

 the madrepores have something analogous to 

 this in the arrangement of their partitions, so 

 that I am tempted to believe that this tend- 

 ency to a symmetrical arrangement of parts 

 in pairs, is a general character of polyps, dis- 

 guised by their radiating form. Among the 

 medusae something similar exists in the dis- 

 position of the marginal appendages and the 

 ocelli. I attach the more importance to these 

 observations, because they may lead to a 

 clearer perception than we have yet reached 



