166 AFFINITIES AND GEOGRAPHICAL 



structure, mostly inhabitants of the waters, many of them pro- 

 pagating not by ova, but by division of their bodies, or by the 

 throwing out of little bud-like excrescences. In this lower 

 region are comprehended the Infusory animalcules, Internal 

 Parasites (Eniozoa), Sponges, Polyps, Sea-nettles (Acalephee), 

 and some other obscure classes. Some of these appear to be 

 distinct and independent series, which advance no further ; 

 such, in particular, are the internal parasites, which necessarily 

 do not pass to any higher grade, because they have no sphere 

 for further development. Others form the roots, as it were, of 

 higher families. 



There are two admitted methods of investigating the affini- 

 ties of beings. One is to observe the connexion between the 

 forms of the mature organisms ; another is to examine the em- 

 bryotic progress, and watch the succession of forms there pre- 

 sented. It is ascertained that no animal, in the course of its 

 development, passes through the forms of all the animals 

 meaner than itself. For example, the sea-nettle is at one time 

 like the monad, an infusory animalcule, and then like the 

 polyp ; the mollusk is successively like the monad and polyp, 

 but never like the sea-nettle. The articulate animal, again, is 

 never like the polyp or sea-nettle, but proceeds at once from 

 the monad form to that of the worm. This Professor Owen 

 calls being " obedient to the law of unity of organization only 

 in its monad stage." 1 The fact has been held as a difficulty in 

 the way of the doctrine of unity ; but perhaps it is only one 

 of the same nature with that intimated regarding the assumed 

 scale of being. I see animals classed by their afiinities in dis- 

 tinct lines, or series, which I regard as stirpes or races. I 

 would therefore expect the unity of organization to be liable 

 to some such limitation as Mr. Owen points out. Is it not, in 

 reality, that each stirps has a unity of organization for itself, or, 

 in other words, that there is such a unity only as far as each 

 particular series of animals is concerned ? These breaks in 

 unity, and the breaks in the chain of being, are but one thing : 

 they are only disturbances to our preconceived ideas, not to a 

 true view of nature drawn from its realities. 



I shall not attempt to place all these obscure animals in 

 genealogical series. The state of zoological science demands 

 that such an effort should be postponed. Let us limit our at- 

 tention to one class, the Echinodermata, or star-fishes, which 



1 Lectures on the Invertebrate Animals, p. 369. 



