268 THE INTERCHANGEABLE RELATIONS OF 



But I have demonstrated (p. 177) that this so-called radiation 

 is merely a lateral repetition of parts, and I have also shown, 

 that, among the highest forms of these ZoopJiytes, this repetition 

 is less and less frequent, and that bilaterality is consequently 

 more clear to the view. 



Now, as we see the two ideas, represented by bilaterality on 

 the one hand, and the type of a grand division on the other, 

 mutually and alternately intensified, and bearing such a variety 

 of degrees of the prominence of the one or the other; so may 

 we also detect a similar relation between these two ideas and 

 the characteristic features which blood relationship transmits 

 from family to family. Will any one undertake to show how 

 bilaterality is propagated from parent to offspring, if it is not an 

 inheritance by blood; but if it is an inheritance by blood, at 

 what point, then, does it cease to be altogether ideal in relation, 

 and begin to be hereditary ? I think it would be just as difficult 

 to answer this question, as it would be to show where the ideal 

 relation of the Lepidosiren to the Fish or the Reptile begins, and 

 where the relation by consanguinity terminates. 



I think I can illustrate the complicated interchanges of these 

 ideas to the fullest extent by explaining the nature of the rela- 

 tions of the animals which are arranged here. It is a group of 

 Articulate animals. Judging from their forms alone, you might 

 conclude that there are several family types represented ; for 

 instance, the worms seem to be illustrated in one place (Ling-ua- 

 tula, fig. 170 (A); Dendroccehim, fig. 182 (M)}, and the spiders 

 (fig. 176 (G)) in another. Others you might take for caterpillars 

 (Tardigrada, fig. 178 (I)), and some for shrimps (Squamella, fig. 

 184 (O), and Cyclops, fig. 185 (P)). Now I could not say posi- 

 tively whether you would be right or wrong in some instances ; 

 for the very reason that several of these animals are related in 

 intermediate ways to more than one family, and in a very com- 

 plicated form of relation. On this account I will undertake 

 to point out but a few of the features which characterize them ; 

 and in order that I may do this in the simplest, systematic man- 

 ner, I have jotted down a tabulated arrangement of characters, 

 which I will endeavor to illustrate by these figures. 



