420 



J. GRAY 



and by McClendon (25) were inadequate, yet the facts appeared 

 to indicate that the activation of the egg, by a spermatozoon, 

 or by artificial parthenogenetic agents, was essentially a physical 

 rather than a chemical process. It now seems possible to put 

 forward a more comprehensive scheme. 



The activation of a resting cell, by contact with another cell 

 in a state of activity, is not limited to the reproductive cells. 

 All contractile cells exhibit the same phenomenon ; if localized 

 fibres at tlie surface of a large muscle are stimulated, the whole 

 of the muscle is rapidly thrown into a state of activity ; the 

 ciliated combs of Pleurobrachia illustrate the same fact 

 (Gray, 10) ; also cells in contact with each other usually divide 

 at the same moment. There can be no doubt that such 

 co-ordination of activity is due to the responsive cells them- 

 selves, and is not due to any nervous or controlling influence. 

 Thus spermatozoa in contact with each other rapidly acquire 

 a synchronous rhythm ; similar examples are readily found 

 in the case of ciliary or muscular elements. 



There can be but little doubt that the influence of one cell 

 upon the activities of its neiglibours has a very profound 

 bearing on the behaviour of the animal as a whole. There is, 

 however, no reason to regard such co-ordination as essentially 

 vital, since a ready parallel is found in inorganic systems. 

 Ostwald (27) found that when a strip of chromium was placed 

 in hydrochloric acid the hydrogen was evolved at regular 

 periods ; each period of activation was followed by a period of 

 inactivity. This periodic condition of activity and inactivity 

 was quite regular for each strip of metal : different strips of 

 metal were, howe\'er, characterized by periods of different 

 length. If several such strips are placed in a bulk of hydro- 

 chloric acid, the periodicity of each strip exhibits itself ; if, 

 however, the strips are in contact with each other then all the 

 strips exhibit the same uniform periodicity. The activation 

 of a passive atrip of iron by contact with an active piece of the 

 same metal has been discussed by E. S. Lillie (23), and has 

 a close bearing on the present problem. 



The activation of a passive cell or metal by contact with an 



