CONTENTS 



PAGE 



I. GENERAL EVOLUTION 



1. THE ORIGIN AND SIGNIFICANCE OF SPINES 3 



Introduction 3 



Law of Variation 5 



Definition of Terms 9 



Growth of a Spine 10 



Localized Stages of Growth 14 



Compound Spines 16 



Application of Law of Morphogenesis 17 



Ontogeny of a Spinose Individual 18 



Phylogeny of Spinous Forms 23 



Categories of Origin 26 



Conditions or Forces affedting Growth 31 



A. External Stimuli 32 



B. Growth Force . . ... > . .... 34 



C. External Restraint 38 



D. Deficiency of Growth Force 39 



Summary of Causes of Spine Genesis 41 



I. In response to stimuli from the environment act- 

 ing on most exposed parts. (Aj.) .... 42 

 II. As extreme results of progressive differentiation 



of previous structures. (A 2 , B 3 .) . . . . 47 



III. Secondarily as a means of protection and offence. 



(A ft B 4 .) 52 



IV. Secondarily from sexual selection. (A 4 , B 4 .) . 57 

 V. Secondarily from mimetic influences. (A 6 , B 4 .) . 60 



VI. Prolonged development under conditions favor- 

 able for multiplication. (B!.) 64 



VII. By repetition. (B 2 .) 67 



VIII. Restraint of environment causing suppression of 



structures. (C x .) 70 



IX. Mechanical restraint. (C 2 .) 77 



X. Disuse. (C 3 , D 2 .) 80 



XI. Intrinsic suppression of structures and functions. 



D. 86 



