26(5 THE RELATIONS OF BIPOLARITY AND BILATERALITY 



We may observe everywhere in the animal kingdom that a 

 manifold repetition of parts, whether longitudinally as in Polyps, 

 or transversely as in Worms, is attended with an indeterminate 

 relation of individuals: in some cases individuality is distinctly 

 marked, whereas in other instances, and under various forms, 

 the individual is more or less merged into the repeated parts. 



Now in the Articulate animal group, where the repetition of 

 parts is from point to point, along a line, the body is divided 

 into joints, and, as if to exemplify the individual character of 

 these joints, among the lowest intestinal worms, each joint at the 

 period of transverse division is separated from its fellows, and 

 plays, for a time, an independent part (p. 84). Among the 

 aquatic worms I have already shown how a number of joints 

 divide off together and form an individual (p. 80). Nowhere 

 do we find in this grand group a longitudinal self-division, but 

 always, in conformity with the type, a transverse one. 



The Mollusca fully exemplify their type, as one which has 

 a unity of conformation, with neither lateral nor longitudinal 

 repetition of parts ; for they do not possess the faculty of self- 

 dividing. I mean, of course, that they do not, as a rule, take 

 this method to reproduce themselves. It is true that some of 

 the lower groups are compound ; but they become so by a pro- 

 cess which is purely a matter of budding, (p. 243, note,) and 

 not of self-division, properly speaking. The instances of self- 

 division or of fissigemmation, which I have pointed out as occur- 

 ring, not only in Mollusca and Articulata, but even in Verte- 

 brates, when discussing the matter of monstrosities, (p. 85,) were 

 then given merely to show how universal an idea may be in its 

 relations, although its practical and normal effects are confined 

 to a more or less circumscribed circle. 



Even the idea of bilaterality is involved with that of reproduc- 

 tion, and the manner in which this relation manifests itself, shows 

 that the idea of a right and a left may possibly be the expression 

 of two individuals united side by side, instead of the duplication 

 of the organs of one individual. I have already referred (p. 85) 

 to the remarkable investigations of Lereboullet upon the embry- 

 ology of the Fish. Without stopping now to go into the details 



