54 M?'. W. S. Mac LE A¥ on certain general Laws regulating 



strictissimfe circumscriptas, tantum circulos plus minus clauses^ 

 affines vero ubique tangentes. Hos tribus, genera, sectiones, &c* 

 simulque si naturae 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 disco- 

 vered ; a conclusion to which we readily arrive on considering 

 how little 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 con- 

 sequence of revolutions undergone by the surface of this globe. 

 Whether one only or both of these reasons be requisite to ac- 

 count 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 meana 

 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*. Thus the series of the Systema Natura 

 and of the Regne Animal is not natural where the Cetacea 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 saltvs 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 naturalist but the ordinary observer. In the 



* It is to be regretted that Professor Dugald Stewart should have been led into this 

 common error, and thus have acquired a somewhat erroneous notion of the law of con- 

 tinuity as it refers to natural history. See the second part of his admirable Disserta- 

 tion, as prefixed to vol. v. of the Supplement to the Encydopadia Britannica, 



other 



