THE BIONOMICS OF CONVOLUTA ROSOOFFENSIS. 411 



condition of the animal, which condition has been induced 

 among other things by all the antecedent light-stimuli acting 

 not only on the reflex mechanism, but upon the whole nervous 

 mechanism. 



Nevei'theless, in the broad way nature uses, the influence of 

 light makes itself felt. This is evident when we consider 

 that the Convoluta zone is the most favoured zone with 

 respect to light consistent with a continuous flow of water; so 

 that if Convoluta were sown broadcast over the beach, 

 those that escaped destruction would inevitably find them- 

 selves brought by the moving waters to this zone. We must 

 therefore conclude that the tropisms of Convoluta are all 

 co-ordinated ; and that just as the mark of a single reflex 

 is its purposefulness, so is purposefulness the character of the 

 co-ordinated tropisms. 



We may sum up the matter thus : — Geotropism in relation 

 to stillness or vibration provides for the vertical distribution 

 of Convoluta, bringing it to the surface when the water is 

 withdrawn, and hurrying it from the surface when the 

 waters flow. The need for a film of water and for not too 

 strong a flow, together with the inertia which a dutiful 

 obedience to its many tropisms involves, and the power of 

 sticking closely to its fellows, all make for the gregarious and 

 localised habit that Convoluta roscof fensis adopts. Rapid 

 streams of water, produced by local changes in the physical 

 condition of the beach, mark out the barren portions of the 

 zone, and may play havoc with the colony. Thus the dis- 

 tribution, like many distributions, is casual, and the " in- 

 stinct '^ of the animal is in favour of parochialism. The 

 young, though capable of swimming freely, remain with the 

 parent colonies, possibly because of the rapidity with which, 

 as we have seen (p. 404), they acquire these tropisms, and also 

 because of their greater power of adhesion to a solid surface 

 in resjjonse to the shock of a sudden current of water.^ 



* Mitsukuri (1901) discusses the influence of light and water on the dis- 

 tribution of Lit tor in a, a case with sonic analogy to Convoluta. 



