128 Animal Life and Intelligence. 



organism, we have to face the difiSculty of understanding 

 how the influence of cells other than those partaking in 

 the regrowth can be brought to bear on these so as to 

 direct their lines of development. If we say that the 

 organism is pervaded by a principle of symmetry such 

 that both growth and regrowth, whenever they take place, 

 are constrained to follow the lines of ancestral symmetry, 

 we are really doing little more than restating the facts 

 without affording any real organic explanation. That 

 which we want to know is in what organic way this sym- 

 metrical growth is effected — how the hereditary tendency is 

 transmitted through the nuclear network which is concerned 

 in cell-division. I do not think that we are at present in 

 a position to give a satisfactory answer to this question. 



Let us now return to the hydra, the artificial fission of 

 which has suggested these considerations. Multiplication 

 in this way is probably abnormal. Under suitable con- 

 ditions, however, if well fed, the hydra normally multiplies 

 by budding. At some spot, generally not far from the 

 " foot," or base of attachment, a little swelling occurs, and 

 the growth of the cells in this region takes such lines that 

 a new hydra is formed. This is at first in direct con- 

 nection with the parent stem, the two having a common 

 internal cavity ; but eventually it separates and lives a free 

 existence as a distinct organism (see Fig. 9, p. 45). 



Now, here we may notice, as an implication from these 

 facts, that the size of the organism is limited. When the 

 normal limits of size are reached, any further assimilation 

 of nutriment ministers, not to the further growth of the 

 organism, but to the formation of a new outgrowth, or 

 bud. What determines that the outgrowth, or bud, should 

 originate in this or that group of cells, we do not know. 

 But, like the isolated fragment in the hydra subdivided 

 by fission, the little group in which budding commences 

 contains a fair sample of the various kinds of cells which 

 constitute the hydra. And here, too, we see that their 

 growth and development follow definite lines of hereditary 

 symmetry. 



