Miscellaneous. 467 



least chiefly) to take place in the heart : on this point fresh obser- 

 vations on living animals, which I have not at the present moment 

 at my disposal, are much to be desired. — ZoologiscJier Anzeiger, 

 xiv. Jahrg., no. 357, Feb. 23, 1891, pp. 78-80. 



The Function of the Gemmiform Pedicellctrice of Sea-Urchins. 

 By M. Henri Pkoitho. 



Since the pedicellaria3 of Sea-Urchins were described by 0. F. 

 Midler the nature and functions of these singular organs have been 

 explained in very different ways. In a paper on certain Echinoids 

 from our own coasts * I asked myself what the role of the pedicel- 

 larise was ; and not being able at the moment to make a statement 

 based upon definite observation, I had to content myself with tho 

 only probable hypothesis, and consider the pedicellarise to be organs 

 of defence. To-day I have the honour of submitting to the Academy 

 an observation made in the aquarium of the Arago laboratory, which 

 may easily be repeated. 



The pedicellarise of the Echinidae were long ago divided into three 

 classes, viz. the ophicephalic, the tridactyle, and the gemmiform. 

 In the present notice we have to concern ourselves with the last of 

 the three only, that is to say with those which exhibit jaws, each 

 provided with a muscular and glandular pouch, the secretion of 

 which issues at the tip, which is terminated by a sort of poison-claw. 

 The head of the gemmiform pedicellarise of Strong ylocentrotus lividus 

 is directly attached to a calcareous stalk articulated to the test ; it 

 is capable of movement on the extremity of this stalk, but it cannot 

 bend down to its base, so that an animal of small size which could 

 glide to the foot of the pedicellaria would be sheltered from its 

 attacks. The gemmiform pedicellaria cannot stoop to seize its 

 enemy, and is therefore at a disadvantage iu protecting the test. 

 Moreover these pedicellarise, which in Strongylocentrotus lividus have 

 a length of 1 centimetre, are scattered through a forest of spines, a 

 very large number of which are as much as 3 to 4 centim. long. If, 

 therefore, a large animal approach the Sea-Urchin to attack it, it 

 would seem that this animal would be protected by the spines 

 themselves against the bites of the pedicellarise. In short the active 

 zone of these organs, which lies above the test and below (he tips of 

 the spines, appears to us, a priori, badly placed, and the ensemble of 

 the facts is well calculated to make us pause ere we consider the 

 gemmiform pedicellarise to be weapons of much effect, notwith- 

 standing their glands and poison-claws. But the difficulty com- 

 pletely disappears when we observe the way in which the Sea-Urchin 

 defends itself by the aid of its gemmiform pedicellarise. 



If in a tub containing one or several specimens of Asterias 

 glacialis, previously kept without food for a considerable period, we 

 place a Strongylocentrotus lividus t, we shall not have long to wait 



* ' Archives de Zoologie experiment ale,' 18S7. 



t The experiment here described I have repeated with Spharechinus 

 gramrfaris, with identically the same results. 



