20 



ASTEROIDEA. 



" With regard to the motions of these Pedicellarics, they not only quickly open and shut 

 the three flaps, but can also turn the head to the different sides, and up and down, and 

 that very quickly. 



" Miiller says, regarding P. tridens : — ' Variat absque aristis, an perditis ?' Of such I 

 have also found a large number of specimens ; but I scarcely believe that they belong to 

 F. tridens, since the teeth of these last are fixed so firmly that they could scarcely 

 fall ofi". Either they are a separate species or a variety of P. triphylla, which they 

 resemble in every point, except that the three flaps are broad at the bottom and small at 

 the ends. These flaps seemed there also to be calcareous, and consisted of many small 

 globules, which were arranged in transverse rows, clearly separated from each other by a 

 light transparent line. Such a line also ran longitudinally down the flap. In P. tripliylla 

 the flaps are not obtuse, but a little rounded, and have, like the foregoing, globules extend- 

 ing in rows. If we now consider the construction of the PediceUarice and their manner of 

 life as a whole, we can scarcely believe them to be anything but organs of the sea-urchin." 



The following reasons seem to prove the accuracy of this opinion : 



" 1st. In all sea-urchins, without exception, are found Pedicellaria, and under the 

 same circumstances ; which would certainly not always be the case if they were parasitical 

 animals, — ^just as Lerncea are not always found in all fishes, &c. 



" 2d. The hard calcareous teeth or plates, and the internal stem, also calcareous, and 

 often filling up alone the sheath, which are found in all Pedicellaria, bear a greater re- 

 semblance to an Echinus spine than to any animal of the Polype kind. There is neither 

 opening, nor mouth, filaments, &c. 



" 3d. The Pedicellaria are firmly fixed in the skin which envelops the whole sea- 

 urchin, upon a very small projecting knob of the shell, to which knob they are very 

 strongly attached, but yet moveable, like the prickles of the sea-urchin ; the under sur- 

 face of the stem of a Pedicellaria being somewhat hollowed and articulated with the knob. 

 When a Pedicellaria is torn out, it is observed that the sheath or skin connecting the 

 stem is torn at the lower end, which, doubtless, is a consequence of its connection with 

 the skin, with which the shell of the sea-urchin is covered, and which, when the Pedi- 

 cellaria is torn out, must be rent. 



" 4th. When the skin of the sea-urchin or a single Pedicellaria is irritated — 

 for example, with a pin — the surrounding Pedicellaria, which stand in a wide circle, in- 

 variably bend themselves quickly towards the irritated part. This phenomenon, which I 

 have often observed, shows clearly an organic connection between the Pedicellaria and the 

 skin of the shell of the sea-urchin. 



" The same thing precisely is observed with the spines." 



On the use of these bodies, M. Sars continues -. " Perhaps Nature, who has so abundantly 

 provided the sea-urchin with such an astonishing number of feet and prickles, has also 

 given the Pedicellaria, as a sort of antennse to seize the small animals which serve for its 

 sustenance, partly to lay hold of whatever might approach their sensitive skin which covers 



