176 NATURAL HISTORY. 



It would be a waste of time and space to point out 

 in detail the extraordinary inconsistencies of such a 

 circular arrangement as exhibited in either of the above 

 schemes. It is enough to point out that passage along 

 such a circular series as either of the above is easy 

 enough and natural enough in a certain direction, and 

 up to a given point; but that it is an impossibility to 

 complete the circle, in consequence of an absolutely im- 

 passable gap between two of the groups in the series. 

 Thus, in the circular arrangement of the whole animal 

 kingdom, as given above, one may pass, without any 

 violation of natural affinities, from the Acrita (the Protozoa 

 of modern naturalists) through the sponges to the Radiata 

 (the Ccelenterate animals and Echinoderms). Through 

 the Echinoderms one may pass from the sea-cucumbers 

 (Holothurians) to the spoon- worms, and thus into the 

 Annulose series; and the passage from the Annulose 

 animals to the Vertebrate animals is at any rate a con- 

 ceivable one. Similarly, in the backward progress, one 

 may pass naturally enough from the Vertebrates to the 

 Molluscs, through the cuttle-fishes (Cephalopods). In 

 order to complete the circle, however, there remains the 

 final step of passing from the Molluscs to the Protozoa 

 (the Acrita), two groups separated by a hiatus unbridged 

 by any intermediate form. 



Similarly, in the circular series of the Vertebrate 

 animals, starting with the Amphibians (frogs and newts) as 

 the assumed lowest group, we pass naturally enough to the 

 reptiles, and from the reptiles to the nearly related group 

 of the birds. From the birds one may get to the Mammals 

 by the help of the oviparous duck-mole and spiny ant- 



