54 Mr.W.S.Maczeay on certain general Laws regulating 
strictissimè circumseriptas, tantum circulos plus minus clausos, 
aflines vero ubique tangentes. Hos tribus, genera, sectiones, &c. 
simulque si naturæ 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 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*. Thus the series of the Systema Nature 
and of the Règne 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 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 naturalist but the ordinary observer. In the 
* [tis 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 Encyclopedia Britannica. 
other 
