280 THE HISTORY OF CREATION. 
CHAPTER XII. 
LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF 
INDIVIDUALS. PHYLOGENY AND ONTOGENY. 
Laws of the Development of Mankind: Differentiation and Perfecting. 
—Mechanical Cause of these two Fundamental Laws.—Progress without 
Differentiation, and Differentiation without Progress.—Origin of 
Rudimentary Organs by Non-use and Discontinuance of Habit.— 
Ontogenesis, or Individual Development of Organisms.—Its General 
Importance.—Ontogeny, or the Individual History of Development of 
Vertebrate Animals, including Man.—The Fructification of the Hgg.— 
Formation of the three Germ Layers.—History of the Development of 
the Central Nervous System, of the Extremities, of the Branchial 
Arches, and of the Tail of Vertebrate Animals.—Causal Connection and 
Parallelism of Ontogenesis and Phylogenesis, that is of the Development 
of Individuals and Tribes.—Causal Connection of the Parallelism of 
Phylogenesis and of Systematic Development.—Parallelism of the three 
Organic Series of Development, 
Ir man wishes to understand his position in nature, and 
to comprehend as natural facts his relations to the 
phenomena of the world cognisable by him, it is abso- 
lutely necessary that he should compare human with extra- 
human phenomena, and, above all, with animal phenomena. 
We have already seen that the exceedingly important 
physiological laws of Inheritance and Adaptation apply to 
the human organism in the same manner as to the animal 
and vegetable kingdoms, and in both cases interact with 
one another. Consequently, natural selection in the struggle 
