THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 



'♦ per litora spargite museum, 



Naiades, et circiim vitreos considite fontes : 

 PoUice virgineo teneros Ific carpite flores : 

 Floribus et pictum, divae, replete canistrum. 

 At vos, o Nymphse Craterides, ite sub undas ; 

 Ite, recurvato variata corallia trunco 

 Vellite muscosis e rupibus, et mihi conchas 

 Ferte, Deae pelagi, et pingui conchylia succo." 



N.Parthenii Gianncttasii Eel. 1. 



No. 73. JANUARY 1854. 



I. — On the Structure of the Echinoderms. 

 By Johannes Muller^'. 



[With a Plate.] 



In addition to their radial form and division, the Echinoderms 

 are essentially characterized by the calcification of their perisoma 

 and of many internal parts, by their peculiar metamorphoses, 

 and especially by their ambulacral organs, feet or suckers, which 

 may be distended by means of a peculiar system of internally 

 ciliated canals. 



The larvje of the Echinoderms are bilaterally symmetrical, 

 and present no trace of a radial arrangement ; when impelled by 

 their cilia, it is always one end which is directed forwards. The 

 radial arrangement is met with only in the adult Echinoderm 

 forms, and even they always present more or less obvious traces 

 of a bilateral symmetry. In those Holothurim which creep upon 

 an ' ambulatory region ^ (Sohle) and in the irregular Echinidce, 

 the bilaterality is at once obvious. But all Echinoderms do not 

 constantly creep on the same surface, or in other words, possess 



* Read before the Royal Academy of Sciences of Bcriin, May 26, 1853. 

 Translated and communicated by Thomas Huxley, F.R.S. 

 Ann. 6f Mac/. N. Hist. Ser. 2. Vol. xiii. 1 



/^ 



