Chap. II. GRADATION AMONG ACALEPHS. 123 



of these two branches. The most natural view seems to me to be that which 

 assigns to them an equal standing, and recognizes their difference in the different 

 tendencies of their plan ; so that, taking the sum of their characteristics, the four 

 primary l)ranches of the animal kingdom should not be placed in one series. 

 Their true relations seem to be best exj)ressed by a diagram like this: — 



VERTEBRATES, 



M L L U S K S , ARTI C U L A T E S , 



RADIATES. 



Again, the different classes of each branch show a relative superiority one above 

 the other. Polyps as a class are certainly inferior to Acalephs as a class, and 

 these, again, inferior to Echinoderms. Acephala as a class are unquestionably 

 inferior to Gasteropoda, and these, again, inferior to Cephalopoda. Worms as a 

 class are certainly inferior to Crustacea, and these in their turn inferior to Insects, 

 etc. And yet there are Worms, such as the higher Annelids, in which the structural 

 complication much exceeds that of the lowest Crustacea, such as the Rotifera. 

 Some Lamellibranchiates are much more highly organized than some of the Phle- 

 benterate Gasteropods. Some of the Fishes may be considered superior to some 

 Batrachian Reptiles ; but no Reptile seems to rise to a level Avith Birds. Here 

 again we see, therefore, that difference of rank is only a secondary feature for 

 classes. The same may be said of families and of genera, as well as of species, and 

 it is much to be lamented that our language has not a greater variety of words 

 to express the many shades of relative standing ; so that Ave are limited to the 

 almost exclusive use of the Avords siijjcrior and inferior, AAdiich are inadequate to 

 render the comparative relations of beings in themselves so exquisitely organized 

 as are the representatives of every class in the animal kingdom. In the groups 

 called orders, hoAvever, the idea of superiority and inferiority seems to be the 

 prevalent feature. Yet orders themselves exhibit also another kind of relations, 

 to Avhich I have already incidentally alluded in an article on the Categories of 

 Analogy, added to the London edition of my Essay on Classification.^ It is curious 

 to observe Iioav the vicAvs entertained by Oken^ respecting certain affinities among 

 annuals, resulting, in his opinion, from the repetition of the same principle in 

 groups of different value, loom up again in the relations of the orders of certain 

 classes to other groups, to Avhich they themselves do not belong. 



If it be true that Hydroids, Discophorte, and Ctenophorte are three distinct 

 orders among Acalephs, it cannot Ije overlooked, that, by their general appearance, 



^ Essay on Classification, by L. Agassiz, London, ^ Compare vol. 1, p. 211. See also Oken's 



1849, 8vo., pp. 271-284. Physio-pliilosopliy, London, 1847, 1 vol. 8vo. 



