I.I GENERAL VIEW. 5 



The mouth is bounded by jaws which open vertically, the 

 nperture itself being extended transversely. 



7. Such being the more significant and general characters 

 of adult man, certain processes and changes of growth may 

 be referred to by which that condition is arrived at. 



A minute rounded, almost structureless mass is the earliest 

 condition of the body. 



The first indication of the future being, which shows itself 

 in that rounded mass, is given by a longitudinal groove mark- 

 ing the place of the spinal marrow and brain. 



Beneath this a similarly longitudinal, cellular rod appears, 

 called the notochord, 1 or chorda dorsalis, marking the place 

 of the future front part of the backbone. 



In process of time the lower jaw appears as a solid rod 

 coming down on each side from the head, and a series of 

 similar structures, called u visceral arches" make their appear- 

 ance on each side, also coming down from the head like the 

 lower jaw, and placed one after the other behind (or, if the 

 body is vertically placed, beneath) that jaw, and forming later 

 the tongue-bone, &c. 



These arches are separated by temporary apertures termed 

 " visceral clefts." 



8. The world is inhabited by a vast animal population, of 

 kinds so numerous and diverse that the study of them would 

 be a task of hopeless difficulty were they not capable of con- 

 venient classification. 



Fortunately they can be and have been divided and 

 arranged, according to their resemblances in form and struc- 

 ture, into a series of more and more subordinate groups. 

 The sum total of animals is spoken of as a kingdom the 

 Animal Kingdom in contrast with and distinction from the 

 Vegetable and Mineral Kingdoms. 



The Animal and Vegetable Kingdoms taken together con- 

 stitute the "organic world," and each member of it is an 

 ''organism." 



The Animal Kingdom is made up of certain great primary 

 groups, each of which is termed a sub-kingdom (or sometimes 

 a division). 



Each sub-kingdom is made up of and is divisible into 

 certain other subordinate (yet still great) groups, each of 

 which is called a class. 



Each class is composed of a certain number of more sub- 

 ordinate divisions, each of which is termed an order. 



1 NCOTOC, back, and x ^/), chord. 



