EXPERIMENTAL MORPHOGENESIS 129 



So we find our formula p.v. (X) =f (s, I, E) very well 

 illustrated in Tiibularia. The formula indeed may help us 

 to predict, in any case, where a certain part of the polyp's 

 organisation is to originate, at least if we know all that is 

 included under our letter E, i.e. the normal proportion of 

 our form. Of course such prediction would not have much 

 practical importance in all our cases of morphogenesis, but 

 nevertheless I should like to state here that it is possible ; 

 for many scientific authors of recent times have urged the 

 opinion that prediction of, and domination over, what will 

 happen, can be the only true aims of sciences at all. 

 myself judge these aims to be of second or third-rate im- 

 portance only, but, if they may be reached by what our 

 purely theoretical study teaches, so much the better. 



Another very typical case of a morphogenetic system 

 of the harmonious type is supplied by the phenomena of 

 restoration in the ascidian Clavellina. I cannot fully 

 describe the organisation of this form (Fig. 13 a), and it 

 must suffice to say that it is very complicated, consisting 

 of two very different chief parts, the branchial apparatus 

 and the so-called intestinal sac ; if these two parts of the 

 body of Clavellina are separated one from the other, each 

 may regenerate the other in the typical way, by budding 

 processes from the wound. But, as to the branchial 

 apparatus, there may happen something very different : 

 it may lose almost all of its organisation and become a 

 small white sphere, consisting only of epithelia correspond- 

 ing to the germ-layers, and of mesenchyme between them, 

 and then, after a certain period of rest, a new organisation 

 will appear. Now this new organisation is not that of a 

 branchial apparatus but represents a very small but com- 



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