CHAPTER VI. 
SYNTHETICAL GROUPING OF VERTEBRATE ANIMALS. 
Having thus indicated the six classes by which I suppose 
the placental class to be surrounded, it becomes necessary 
to show in what manner I propose connecting them. I 
have ventured, at page 12, to suggest that the placentals 
divide into seven tribes, one of which is normal and cen¬ 
tral, three subnormal, and stationed at certain distances 
around the centre, and the remainder abnormal, stationed 
at a greater distance and alternating with the subnormal 
tribes. A similar disposition of the classes seems to me 
in accordance with nature. The placentals form the nor¬ 
mal and central group ; the marsupials, cartilaginous fishes 
and pachydermatous reptiles form the subnormal groups ; 
birds, true fishes and true reptiles form the abnormal 
groups, or, in other words, recede farthest from the central 
and normal form of man. The subnormal and abnormal 
groups appear to alternate with each other in this order, 
— marsupials, birds, cartilaginous fishes, bony fishes, 
reptiles cased in armour, scaly or naked reptiles; and 
the relative mutual similarities of the seven groups may be 
shown thus.— 
