1823.] the natural Distribution of Insects and Pvngi, 329 



which touch other circles. Such only are natural groups. This 

 was said of Insects ;* and our author, looking only at plants, 

 and principally at Fungi, comes to the same conclusion, as ap- 

 pears from the following words : " Species unica in natura fix^ 

 circumscripta idea. Superiores nuUas agnovimus sectiones 

 strictissime circumscriptas, tan turn circulos plus minus clausos, 

 affines vero ubique tangentes. Hos tribus, genera, sectiones, 

 8cc. simulque si naturse vestigia sequuntur, naturales dicimus." 



That the circle, indeed, is not always closed or complete has 

 been observed likewise in the animal kingdom ; and there are two 

 ways of accounting for it. First, that the beings which would 

 render the circle complete have not yet been discovered ; a 

 conclusion to which we readily arrive on considering how httle 

 is yet known of natural productions ; and secondly, that there 

 are hiatus or chasms which do really exist in nature, and which 

 may be attributed to the extinction of species in consequence of 

 revolutions undergone by the surface of this globe. Whether 

 one only or both of these reasons be requisite to account for 

 circles of affinity not always appearing complete, we shall not 

 at present investigate ; contenting ourselves with the undoubted 

 fact, that hiatus or chasms are everywhere in nature presenting 

 themselves to the view. But this truth by no means contradicts 

 the Linnean maxim, that no saltus exists in nature, although 

 such has been esteemed its effect by certain naturalists who 

 have been in the habit of taking the words hiatus and saltus as 

 synonymous terms.f Thus the series of the Si/stema Natura 

 and of the Regne Animal is not natural where the Celacea inter- 

 vene between Quadrupeds and Birds, but is perfectly consonant 

 with nature where the Tortoises are made to follow these last. 

 In the first case, there is a saltus or leap from Quadrupeds to 

 Birds over a group totally dissimilar to the latter ; there is, in 

 short, an unnatural interruption of the law of continuity, which 

 shocks not merely the naturgilist but the ordinary observer. In 

 the other case there is only an hiatus or chasm, which the dis- 

 coveries of a future day may fully occupy. Speaking therefore 

 theoretically, it may be affirmed that a saltus never did exist in 

 nature ; and it also may be argued, with great appearance of 

 truth, that if the hiatus are real which so commonly occur in 

 nature, they did not always exist ; or, in short, as M. Fries 

 expresses himself, " Oninis sectio naturalis circulum per se clan- 

 sum exhibet." 



Now this definition of a natural group could never have been 

 given by any person who was not aware of the distinction to be 

 made between affinity and analogy. But whenever two parallel 



* IJorte Entomohgicce^ p. 459, &c. 



+ It is to bf! regretted that Prof. Dugald Stewart should have been led into this com- 

 mon error, and thus have acquired a somewhat erroneous notion of the law of continuity, 

 as it refers to natural history. See the second part of his admirable Dissertation, as 

 prefixed to vol. v. 6i the Supplement to the Encyclopedia Bntunnica, 



