CILIARY ACTIVITY 37 



ratio antagonises the effect of pure solutions of the monovalent 

 ions on the velocity of amceboid movement, the optimum ratio 

 differing again with the monovalent ion used. Nevertheless, 

 amoeboid movement, which, as stated, ceases in pure solutions 

 of either calcium or magnesium, can be prolonged in mixtures of 

 the two, this antagonism being evidently of a different nature 

 from the antagonism of either to monovalent ions. 



The Pigmentaxy Effector System.— Colour response in cold- 

 blooded vertebrates and Crustacea has been regarded by some 

 investigators as a form of amoeboid activity. The power to 

 respond to environmental influences in changes in bodily 

 colour is also met with in molluscs where the pigmentary 

 organs are muscular structures. In vertebrates and Crustacea 

 colour response is brought about by the dispersion or aggrega- 

 tion of pigment granules in special cells or groups of cells, 

 which may be described as pigmentary effectors to distinguish 

 them from the chromatophores of molluscs. The pigmentary 

 effectors of vertebrates (reptiles, amphibia, and fishes) are 

 unicellular organs charged with pigment granules. Only one 

 type has been subjected to careful experimental investigation — 

 the melanophores or black pigment cells. According to some 

 authors the concentration of pigment granules in the 

 "contracted" condition is associated with the active with- 

 drawal of the cell processes, which are supposed to He in 

 preformed lymph spaces. The majority of recent observers, 

 with the notable exception of Graham Kerr, however, do not 

 regard the process as analogous to amoeboid movement, but 

 consider that the pigment granules stream to and fro within 

 fixed cell processes. 



The co-ordination of vertebrate pigmentary response with 

 environmental agencies will be considered in a later chapter 

 (Chapter VII). Here we are concerned chiefly with the 

 properties of the pigmentary effector as an isolated organ. If 

 the contracile mechanism is one of dispersion and aggregation 

 of granules, it is possible that the visible responses of pig- 

 mentary effectors are more directly related to known properties 

 of colloid systems than those of any of the mechanisms so far 

 discussed. Up to the present there has been little quantitative 



