TO THE FIVE GREAT TYPES. 265 



principle is, as it were, set against itself; the opposing poles are 

 antagonistic only in one sense, though ; they cannot exist the one 

 without the other, any more than can the positive and negative 

 poles of the electrical sphere which wraps this globe in an invis- 

 ible shell. The idea of a balance between these upper and 

 lower poles seems, as a natural consequence, to necessitate the 

 consideration of lateral relations ; and these we find progressively 

 elaborated and set forth in the idea of bilciterality. Everywhere 

 we see the idea of progression, from a lower to a higher, man- 

 ifested in various relations. The ideal relation of progress is 

 that which is the most general. 



And now when we come to the consideration of the charac- 

 teristics of the five grand divisions, we seem to have lighted 

 upon certain ideas which have no relation whatever to the fun- 

 damental idea of the typical animal; it seems at first glance as 

 \ifive neiv seals were impressed upon the original stamp, and 

 obscured or blotted out its distinguishing features; but I am 

 inclined to look upon the matter in another light. You will 

 recollect what I told you some time ago (p. 85) in regard to the 

 tendency of the egg, especially of the lower animals, to divide 

 into two or more, and that in this way the so-called monstrosi- 

 ties among higher animals were formed. You will call to mind, 

 too, that I pointed out the prevalence of the self-dividing- process 

 of reproduction among the lower forms (chap. in. and p. 110). 

 Among the Protozoa (Infusoria) this process takes place in such 

 a way as to not only divide the animal transversely, but also 

 lengthwise ; that is, the creature not only repeats itself by cross- 

 wise division, but also by lengthwise or longitudinal repetition. 



Now how do we see this idea carried out in the groups above 

 Protozoa? In the Zoophyte division we have taken note (p. 61) 

 of the longitudinal splitting of the Polyps, especially of the com- 

 pound forms, the branching corals. Among the single Polyps this 

 splitting totally divides the individual into two; but in the branch- 

 ing corals the splitting only divides the head and stomach, and 

 thus a many-headed creature is formed. The tendency would 

 seem to be to separate the laterally repeated parts, as so many 

 individuals, from each other. 



