282 THEORETICAL BIOLOGY 



receptor as well as of the effector side) each as a single base 

 on which the captain or adjutant forms the apex of a 

 pyramid, we get, as our picture of the whole, a number of 

 pyramids, arising from a common base, and coming together 

 by their apices. 



If now we connect each receptor captain or adjutant 

 with a corresponding effector, we get, as the expression of 

 the steering-mechanism, a bundle of reflex arcs, which, for 

 the majority of animals, suffices to explain their various 

 reactions. The complete structure of representatives as a two- 

 sided system of pyramids connected together by nervous 

 routes, will suffice, however, only for reflex actions. For all 

 other actions, fresh nervous connections must be made ; and, 

 to make these, it is necessary that the impulses invade the 

 protoplasm of the nerve-persons. 



The development of new nerve-persons cannot be demon- 

 strated anywhere ; but what unquestionably happens is the 

 formation of new paths for excitation between those already 

 present. So the nerve-persons must have the power to send 

 out nervous pseudopodia, which serve as permanent or as 

 temporary bridges for the conduction of the excitation. 



This simplifies extraordinarily the problem on which we 

 are engaged : all we have to do is to imagine the nerve- 

 persons in question at the moment as little amoebae, con- 

 nected together by means of a permanent nerve, whether 

 receptor or effector, and having the power to send out pseudo- 

 podia, which fuse with those of other amoebae, and with them 

 form bridges and networks permitting transmission of the 

 excitation. 



The protrusion of a pseudopodium is referable to the 

 activation of a gene. The activation of a gene can take 

 place only through the coming in of an impulse. But the 

 possibility of the activation also depends on external circum- 

 stances ; for instance, there may be a material chemical 



