196 Mr.W. S. MacLeay on coiain general //rttis yrgulaiing 



they not been so designed at the creation. A lehition of ana- 

 logy consists in a correspondence l)ct\veen certain parts of the 

 organization of two animals which <]iffer in their general struc- 

 ture. In short, the test of such a relation is l;arely an evident 

 similarity in some remarkable points of formation, which at 

 first sight give a character to the animals and distinguisli 

 them from others connected Avith them by affinity; whereas, 

 the test of a relation of affinity is its forming part of a transi- 

 tion continued from one structure to another by nerirly equal 

 intervals. As a relation of analogy must always depend on 

 some marked property or peculiarity of structure, and as that 

 of affinity, which connects two groujis, becomes weaker and 

 less visible as these groups are more general, it is not in the 

 least surprising, that what is only an analogical correspondence 

 in one or two important particulars, should often have been 

 mistaken for a general affinity. 



M. Fries draws the distinction between them precisely in the 

 same way, and, making allowance for the difference of the ob- 

 jects he was investigating, almost in the same words : " Natura 

 tamen, ubique varia, semper tamen eadem, hoc est, eandem 

 ideam exponere tendit, mutatis modo, quic ex ulteriori ratione 

 necessario pendent ; eadem sequitur princi}na, ita modo ut in- 

 feriora (v. g. exterior forma, qutc in infimis adhuc vaga) su- 

 perioribus cedant. Errant igitur qui distinctiones sunnrias e 

 forma exteriori tantum ducunt ; quis ex hac regnum animaie 

 et vegetabile definire potuit? Evidentissime hoc demonstrant 

 Lichenes et Fungi. Recentiores, horum differentiam in cha- 

 ractei'ibus extern is tantum ponentes, cum Fungis jungere vo- 

 luerunt Lcprarias, Opegraphas, Calicia, Verrncarias, (Sec. quod 

 nullo modo probare possum. Altius illorum diffi^i^entia de- 

 ducenda. Sed cum natura eadem via inter Lichenes et Fungos 

 ubique progreditur, singulum genus Lichenum Fungis corre- 

 spondet. At haec inde ajjinia non dicimus ; sed analoga. 



" Affinia igitur sunt qua? in eadem serie sequuntur et in se 

 invicem transire videntur. FIobc in ulterioribus congruunt 

 sed in citerioribus rationibus differunt. Analoga autem dici- 

 mus quae in diversis seriebus locis parallelis* posita sunt et 

 sibi invicem correspondent. Ultima cosmica momenta dif- 



* As there is some clanger of being led astray by our imagination when 

 we first attempt to separate relations of analogy from those of affinity, it is 

 fortunate that the naturalist cannot have a more admirable test of his ac- 

 curacy, or a stronger rein on his fancy, than this parallelism of analogous 

 groups in contiguous series of affinity. Thus, although a solitary resem- 

 blance may mislead, it is clear that when we find several of such resem- 

 blances to keep parallel to each other in contiguous scries, we may reckon 

 upon their having some more soliil foundation than our own fancy. 



ferunt, 



