4 
The Protozoa — as sponges and infusoria — the lowest fornas 
of animal life, many of them microscopic and bordering 
closely on the vegetable world. 
It is with the first division only that the collection in the 
Garden has to deal. The Vertebrates — animals possessing a 
skeleton of bone or cartilage, enclosing cavities in which 
the soft parts of their organization are contained and pro- 
tected from injury — are arranged in five classes, according to 
the nearness with which they approach to one of the five 
great types of structure which have been found to exist 
among them : — 
I. Mammalia — animals which suckle their young. 
II. Aves, or birds. 
III. Patrachia — as frogs, toads, and salamanders. 
IV. Reptilia — as turtles, lizards, and serpents. 
V. Pisces, or fishes. 
These classes are again broken up into orders, each posses- 
sing an association of structural characters which is common 
to all the individuals included in it, and in which they differ 
from all other individuals in their class. These orders have 
been differently constituted and arranged, according as differ- 
ent points have been made use of for their determination. 
They are again divided into smaller groups called families, 
which, possessing the characteristic mark of their order, yet 
depart in some minor consideration from its type — or, in 
other words, from that form which has been taken to show 
most clearly the peculiarity of the order. 
Families are again broken up into genera, which bear to 
them much the same relation as that which they, in turn, 
bear to orders. Thus — to illustrate with a familiar example — 
the lion, tiger, panther, &c. are all cats and belong to one 
genus — Felis ; they are classified as follows : — 
Division Vertebrata — because they have a backbone or ver- 
tebral column. 
Class Mammalia — because they have organs peculiar to 
those animals which suckle their yonng. 
Order Carnivora — because their plan of structure is that 
possessed by animals which live on flesh. 
Family because, in addition to the above, they 
possess a common arrangement of teeth, claws, and other 
structural points, which none of the other carnivora share. 
Genus Felis — because certain minor modifications are un- 
like those existing in a few more individuals, which so far 
