52 Mr. W. S. Macleay on certain general Laws regulating 



on some marked property or peculiarity of structure, and as that 

 of affinity, which connects two groups, 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, quae ex ulteriori ratione 

 necessario pendent ; eadem sequitur principia, ita modo ut infe- 

 riora (v. g. exterior forma, quae in infimis adhuc vaga) superiori- 

 bus cedant. Errant igitur qui distinctiones summas e formd 

 exteriori tantum ducunt ; quis ex hac regnum animale et vege- 

 tabile definire potuit ? Evidentissimfe hoc demonstrant Lichenes 

 et Fungi. Recentiores horum difFerentiam in characteribus ex- 

 ternis tantum poneiltes cum Fungis jungere voluerunt Leprarias, 

 Opegraphas, Calicia, Verrucarias, &c. quod nuUo modo probare 

 possum. Altius illorum differentia deducenda, Sed cum na- 

 tura e4dem vi4 inter Lichenes et Fungos ubique progreditur, 

 singulum genus Lichenum Fungis correspondet. At haec inde 

 affinia non dicimus ; sed analoga. 



"Affinia igitur sunt quae in eadem serie sequuntur et in se in- 

 vicem transire videntur. Haec in ulterioribus congruunt sed in 

 citerioribus rationibus differunt. Analoga autem dicimus quae 

 in diversis seriebus locis parallelis* posita sunt et sibi invicem 



corre- 



* As there is some danger of being led astray by our imagination when we first at- 

 tempt to separate relations of analogy from those of affinity, it is fortunate that the na- 

 turalist cannot have a more admirable test of his accuracy, or a stronger rein on his 

 fancy, than this parallelism of analogous groups in contiguous series of affinity. Thus, 



although 



