468 Miscellaneous. 



before we see it attacked by the Starfishes. As soon as the Urchin 

 feels the contact of the ambulacral tentacles of the Starfish attempt- 

 ing to seize it, it quickly lowers the spines of the region menaced. 

 These spines take up a slanting radial position round the centre of- 

 the attack, and they are so completely inclined that the majority 

 of them become almost tangents to the test. By thus lowering its 

 spines the Urchin unmasks its gemmiform pedicellarioe, which we 

 now observe extended towards the arm of the Starfish, and presenting 

 to it their widely open jaws. The Asterias continues the attack ; 

 but as soon as one of its sucker- feet touches the head of a pedicel- 

 laria, it is immediately bitten, and we can but conclude that the 

 pain occasioned by the bite is very keen, for the arm of the starfish 

 is precipitately withdrawn. In retracting, the sucker-foot which 

 has been bitten always carries away the pedicellaria fixed in the 

 wound. 



Sometimes the first bites suffice to repulse the Asterias ; but on 

 other occasions the latter continues the attack, and then it becomes 

 a realty interesting sight to watch the Urchin unmasking its pedi- 

 cellarias at all the points of attack, and, if I may be permitted to use 

 the expression, thus following the movements of its enemy by showing- 

 its teeth. In a first encounter the advantage always rests with the 

 Urchin, and the Asterias retires riddled with wounds ; but since 

 each pedicellaria only serves a single time in the defence of the Sea- 

 Urchin, since it leaves its jaws in the wound, the Urchin by degrees 

 exhausts its means of defence. If therefore we leave a Sea- Urchin 

 in a tub with several Starfishes, and the latter continue the assault, 

 the Urchin succumbs to its fate ; but the issue of the combat is for 

 us a matter of secondary moment. The manner in which the Urchin 

 unmasks its weapons, which are ordinarily concealed and protected 

 by the spines, appears to me, on the other hand, particularly worthy 

 of attention. 



As soon as the Urchin is apprised, by means of its peripheral 

 nervous system, of the danger which menaces it, it communicates to 

 its spines a movement which has nothing in common with the cus- 

 tomary movements of these organs, and the sole object of which is to 

 bring the jaws of its gemmiform pedicellarise to bear on the enemy. 

 It is interesting to note that this movement of the spines is precisely 

 the opposite of that which takes place if we wound the surface of the 

 test with the point of a needle for instance. In this case spines and 

 pediecllariae incline towards the wounded spot. On the contrary, 

 when the Urchin assumes a defensive position it withdraws the spines 

 from the point menaced, at the same time directing towards its 

 enemy its pedicellariae, which are thus unmasked and the jaws of 

 which are ready to bite. In this case it is not a local pain, but a 

 more complex sensation which we cannot analyze, which provokes 

 a combination of movements undeniably interesting in a creature so 

 low in the scale. — Archives de Zoologie expenmeatale et generate, 

 ser. 2, t. viii., Annce 1890, no. 4, pp. xlii-xliv (Comptes Mendus, 

 cxi. (1890), pp. 62-64). 



