ECHINODERMATA. 7 



incessantly the interior of the body, and to perforin an important part in the function of 

 respiration ; their blood is circulated in arteries and veins, aided by a central pulsating 

 organ or heart. The five ovaries and testicles occupy the ambulacra! divisions, and open 

 externally through the holes in the genital plates. Their locomotion is effected by the 

 joint action of the tubular retractile suckers and the spines. Many sea-urchins attach 

 themselves to rocks by these tubular feet, and some bury themselves in limestone, and 

 sandstone or even in granitic rocks, by the abrading action of the spines.* 



The nervous system consists, according to M. Van Beneden, of a circular cord, which 

 surrounds the entrance to the digestive organs, and sends branches into the divisions of 

 the body. Professor Agassiz, and the late Professor Edward Forbes, regarded the organs 

 situated in the ocular plates as eyes, but M. Dujardinf denies them even a nervous system. 

 In the absence of a greater amount of direct anatomical evidence on the point, the follow- 

 ing observation, related by M. Alcide d'Orbigny,j has an important bearing on the 

 question, and supports it affirmatively. 



Captain Ferdinand de Cande, who commanded the ' Cleopatre ' in the Chinese seas, 

 told M. d'Orbigny that he had captured, on their coasts, an urchin with long spines, 

 probably a Diadema, which he examined in a vessel of water. " I hastened to seize it," he 

 observed, " when it instantly turned all its spines in the direction of my hand, as if to 

 defend itself. 



" Surprised at this manoeuvre, I made an attempt to seize it on the other side, when 

 immediately the spines were directed towards me. 



" I thought from this that the urchin saw me, and that the motion of the spines was 

 intended as an act of self-defence ; but, to prove whether this movement of the animal 



* M. Eugene Robert exhibited to the Academy a block of old red sandstone, obtained from the shore 

 of the great Bay of Douarnenez, •which was perforated with numerous holes, evidently formed by the 

 Echini which were lodged in them. Each rounded cavity is in exact proportion, both as to size aud form, 

 with the body of the Echinoderm. M. Lory, Professor at Grenoble, and well known for his numerous and 

 excellent works on geology, has begged me to exhibit several specimens of perforating Echini, which have 

 taken up their abode in the granite of the Bay of Croisic, not far from Piriac. It is the same granite as that 

 from the Pouliguen, and in the same state of alteration. This igneous rock is there perforated by Mollusca 

 and Echinodermata for an extent of several kilometers. Those which M. Lory has just discovered are 

 certainly of the same species as the Echini which burrow in the old red sandstone of the Bay of Douarnenez. 

 They closely resemble the Mediterranean Echinus, mentioned by Lamarck under the name of Echinus lividus. 

 It is one of the most abundant Echini on the coast, and in the market of Marseilles, whence Lamarck 

 obtained his specimens. I have never heard that these individuals possessed perforating habits ; and 

 probably a careful examination of living specimens of the Echinus from the coast of Brittany may show 

 that it belongs to a distinct species, notwithstanding its apparent identity with that of the Mediterranean. 

 In this case it might be called Echinus terebrans. 'Observations on Echini perforating the Granite of 

 Brittany,' by M. Valenciennes. — Comptes Rendus, Nov. 5, 1855, p. 755. 



f Lamarck, ' Animaux sans Vertebres,' 2d ed., torn, iii, p. 200. 



X ' Paleontologie Francaise Terrains Oretaces,' torn, vi, p. 12. 



