Remarks on Zoological Classification. 413 



to work from such a form as a centre, in opposite directions. 

 Mr. MacLeay has well laid down this law, and shown a ten- 

 dency to re-entering or Circulating forms, and has placed the 

 whole Animal Kingdom under five divisions : — 



ACRITA, 

 MOLLUSC A, 

 VERTEBRATA, 

 ANNULOSA, 

 RADIATA. 



The principle is undoubtedly sound, though his Quinary sys- 

 tem may be pushed beyond its just limits, and the materials 

 of the circle may not be quite correctly arranged. 



3. It would appear moreover, that natural series do not 

 merely tend to re-enter, but that the alliances at equal dis- 

 tances from two extremes, may be in some degree parallel 

 or related to each other, as if the series rose to a certain 

 point, and then descended at the same rate, through analo- 

 gous structures. 



4. In making this attempt, it was impossible to avoid re- 

 ference to the shape of the developement of other organized 

 bodies, as exhibited in the two parallel botanical races, but it 

 was proper to renounce any expectation of finding the same 

 number of alliances here, and also to leave it an open ques- 

 tion, whether the zoological alliances formed one, two, three, 

 or more independent Races. It now appears that these con- 

 stitute a single re-entering race, of which the alliances at e- 

 qual distances from the extreme points, offer analogies. I 

 cannot therefore conceal from myself, that the two botanical 

 races may also constitute a single Race, connected by the Rhi- 

 zanths and some of the Endogens at one extremity, or parting 

 in opposite directions from Fungoid structures at the other. — 

 Such suppositions will not in any way affect the existing ar- 

 rangement. 



5. It was necessary in this investigation to presume the 

 possibility, that certain great divisions recognized in Zoology, 

 might, as in Botany, form the parallel portions of two diffe- 

 rent series. It seems however that the Mammalia, Aves, and 

 Insecta, are not so divided ; and the impossibility of finding 

 four distinct points in each, by which each might connect 

 with some other assemblage, proved their unity. On the other 

 hand it was not difficult to see that the Amphibia and Pisces 

 are so divisible. The Acephalous Conchifera and the Mollus- 

 ca proper have been lately united, but it would appear with- 

 out sufficient reason. The separation of the Entozoa from 

 the Radiata, and the Crustaceous families from the Insecta 



