674 SCIENCE PROGRESS 



due to reaction to obvious stimuli, whether a nervous system be 

 present or not. There is however a manifestation of co-ordina- 

 tion which has met with comparatively little attention which is 

 not connected with reaction to obvious stimuli ; it would appear 

 to be an inherent characteristic of living matter when in the 

 form of multicellular organisms and is far more subtle than the 

 phenomena already mentioned. 



Multicellular organisms commence their existence as single 

 cells. 1 In the majority of cases these single cells are formed by 

 the fusion of two cells — generally derived from separate indi- 

 viduals — which after fusion into single cells are known as 

 fertilised ova. The fertilised ovum divides into two cells, each 

 of these divides again and this process of division goes on until 

 the whole organism is built up. In the early stages the cells 

 produced from the division of the fertilised ovum are known as 

 blastomeres. If a fertilised ovum of Triton, Amphioxus or 

 certain other animals be taken at a stage when it has segmented 

 into, say, four blastomeres and the blastomeres be shaken apart, 

 each of the separate blastomeres — which we will for the sake of 

 convenience designate as A, B, C and D — will develop into an 

 embryo proportionately smaller than the embryo produced from 

 the whole ovum but complete in all its parts. 2 What is the 

 significance of this fact? It means that each blastomere is 

 capable of producing all the tissues of the body — that the cells 

 derived from each give rise to all the various types that are 

 found in the organism. But it means much more than this. 

 If the blastomeres be left together and the ovum be allowed 

 to develop in the ordinary manner, the cells descended from 

 A do not include all the types of cells that are produced by 

 B, C and D. It follows that A, which has the potentiality of 

 producing all that in the ordinary course of events would be 

 produced by B, C and D, does not do so when it forms part 

 of a multicellular individual. It proves that there is a common 

 influence dominating the cells forming a multicellular individual 

 which causes them to be in some respects interdependent and, 

 under normal conditions, limits the lines along which differentia- 



1 The cases in which new individuals are produced from buds or cuttings do not 

 affect the general argument here advanced. 



2 Driesch, H., Analytische Theorie der Organise/ten Entwicklwig, Leipzig, 1894 ; 

 Morgan, T. H., Anat. Anz. x. 19, 1895 > Wilson, E. B., Arch. f. Entwick. iii. 1, 

 1896 ; and many others. 



