ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
611 
Function of Madreporic Plate and Stone-canal of Echinodermata.* 
—Prof. II. Ludwig altogether denies the accuracy of Prof. M. Hartog’s 
observation that the direction of the current is from within outwards in 
the pore canaliculi of the madreporic plate and in the interior of the 
stone-canal. Prof. Ludwig took the opportunity of a visit to Naples to 
investigate the point in Holothuria tubulosa, Stichopus regalis , Sphserechinus 
granularis, Aster ina gibbosa and A. Pancerii , Antedon rosacea , and some 
Auriculariae. In all cases he found the direction of the stream to be 
from without inwards, and he gives details of his observations in support 
of his generalization. 
M. L. Cuenot j answers Prof. Hartog’s note of reclamation,^ and 
gives reasons for not noticing his work, and then proceeds to raise 
certain objections to Prof. Hartog’s view as to the nephridial function 
of the madreporic system. 
Function of Gemmiform Pedicellarice of Echinoids.§ — M. H. 
Prouho contributes a very interesting observation to the very vexed 
question of the functions of pedicellariae. If a specimen of Strongylo- 
centrotus lividus or Sphserechinus granularis be placed in a vessel in which 
there are one or more specimens of Asterias glacialis which have been 
compelled to fast for some time, the Echinoid will be immediately 
attacked by the starfishes. As soon as it feels the touch of their ambu- 
lacral tubes it rapidly withdraws its spines from the part threatened ; 
the spines bend out from the centre of attack to so great an angle that 
they become almost tangential to the test. In thus removing its spines 
the urchin unmasks its geramiform pedicellariae, which are then stretched 
towards the arms of the starfish with the jaws widely open. The star- 
fish continues its attack, but as soon as one of the pedicellariae touch an 
ambulacral tube it immediately bites it ; we may suppose that the pain 
produced is considerable, for the arm of the starfish is actively with- 
drawn ; but it always carries with it the offending pedicellaria fixed in 
the wound. 
In some cases the first bites are sufficient to drive off the starfish, 
but in others it prolongs its attack, and then it is very interesting 
to see the urchin unmask its pedicellariae on the points attacked, and, so 
to speak, follow the movements of its enemy by showing its teeth. In 
a first fight the victory is always with the urchin, and the starfish retires 
covered with wounds. But, as each pedicellaria serves only once for 
the defence of the urchin, it is gradually deprived of its organs for this 
purpose. If an urchin is put with several starfishes and abandoned to 
its fate it succumbs at last. 
The moment an Echinoid is warned by its peripheral nervous system 
of the danger which threatens it, it moves its spines in a way which has 
nothing in common with the ordinary movements of these organs, and 
which has no other object than to unmask its gemmiform pedicellariae. 
It is of interest to observe that this movement is exactly the opposite of 
that which is produced when the surface of the test is wounded by, for 
example, the point of a needle ; in that case the spines and pedicellariae 
are inclined towards the wounded point. 
* Zool. Anzeig., xiii. (1890) pp. 377 9. 
f T. c., pp. 315-8. 
§ Coroptes Rendus, cxi. (1899) pp. G2-4. 
t See this Journal, ante , p. 337. 
