140 • HABIT AND INTELLIGENCE. [CHAP. 



and among them, if one tentacle is irritatedj the rest will 

 contract instantaneously.^ 



As already stated, the parts of organisms in which nutri- 

 tive processes go on (as, for instance, young buds, animal 

 and vegetable embryos, and secreting organs) mostly con- 

 sist of cellular tissue ; and vascular structures, among 

 vegetables certainly,^ and probably among animals also, 

 consist of modified cells. This is shown both by the 

 Develop- history of their development among the higher vegetables, 

 ™ ssels out ^^^ ^y ^^^ ^^*^^ ^^^^ among the higher fungi and lichens 

 of cells, we meet with cells elongated in the direction of the length 

 of the stem, which are evidently a transition from simply 

 cellular to vascular structure.^ Cellular and vascular struc- 

 tures are thus probably akin ; and the parallel relation 

 Eesem- between muscle and nerve is, I think, shown (though I do 

 nervous'^ not wish to lay any stress on this) by the resemblance of 

 fibre to the minute structure of nervous fibre to that of muscular 



muscular, rj-i 4 



But the parallelism of the circulatory and nervous 



systems is far more unmistakeably shown in various other 



Blood- ways. Tlie nerves and the blood-vessels resemble each 



vessels and other in ramifying and inosculating ^ throughout the entire 



nerves ./ o o o 



ramify. body; and also in this, that the action of both is in a great 

 degree (though, as careful researches have shown, not abso- 

 lutely) controlled by great central organs ; the circulatory 



The heart system by the heart, and the nervous system by the brain. 



brain. Circulatory centralization and nervous centralization, as 

 they may be called, are seen to increase together as we 

 ascend in the animal scale : that is to say, the higher is 

 the organization of any animal, the more complete is the 

 centralization both of its circulatory system, and conse- 

 quently of its nutritive or vegetative life, — and of its 

 nervous system, and consequently of its animal life. It is 



1 Spencer's Piinciples of Biologj-, vol. ii. p. 368. = j]jj(j_ p 254. 



^ Carpenter's Comparative Physiology, p. 671. 



* For the fact of this resemblance, see Beale's edition of Todd and 

 Bowman's Physiology, p. 72, 



^ To inosculate means to reunite after ramifying. But though nerve 

 trunks ramify and inosculate, it is believed that the ultimate nerve-/5/-es 

 remain always distinct. 



