XX 



INTRODUCTION. 



Ill Embryology, 



The doctrine of the generation and development of organisms. 



History of the develop- 

 ment of single beings, 

 of the individual (.e.g., 

 of man) from the ovum 



onwards (Ontogeny) : 



(a) In Plants, 

 (6) In Animals. 



Morphological part of the 

 doctrine of develop- 

 ment, i.e., the doctrine 

 of form in its stages of 

 development 



(a) General, 



(6) Special. 



Physiological part of the 

 doctrine of develop- 

 ment, i.e., the doctrine 

 of the activity during 

 development 



(a) General, 



(6) Special. 



2. History of the develop- 

 ment of a whole stock 

 of organisms from the 

 lowest forms of the 

 series upwards (Phy- 



logeny) 



(a) In Plants, 



(b) In Animals. 



Morphology and Physiology are of equal rank in biological science, 

 and a previous acquaintance with Morphology is assumed as a basis 

 for the comprehension of Physiology, since the work of an organ 

 can only be properly understood when its external form and its 

 internal arrangements are known. Development occupies a middle 

 place between Morphology and Physiology; it is a morphological 

 discipline in so far as it is concerned with the description of the parts 

 of the developing organism ; it is a physiological doctrine in so far 

 as it studies the activities and vital phenomena during the course of 

 development. 



Matter. 



The entire visible world, including all organisms, consists of 

 matter, i.e. 9 of substance which occupies space. 



We distinguish ponderable matter which has weight, and imponderable 

 matter which cannot be weighed in a balance. The latter is generally 

 termed ether. 



In ponderable materials, again, we distinguish their form, i.e., the 

 nature of their limiting surfaces; further, their volume, i.e., the 

 amount of space which they occupy; and lastly, their aggregate condition, 

 i.e., whether they are solid, fluid, or gaseous bodies. 



Ether. The ether fills the space of the universe, certainly as far 

 as the most distant visible stars. This ether, notwithstanding its 

 imponderability, possesses distinct mechanical properties ; it is infinitely 

 more attenuated than any known kind of gas, and behaves more like 



