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 affecting 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. (Aj, Bs.) .... 47 



III. Secondarily as a means of protection and offence. 



(As, B,.) 52 



IV. Secondarily from sexual selection. (A4, B4.) . 57 

 V. Secondarily from mimetic influences. (A5, B4.). 60 



VI. Prolonged development under conditions favor- 

 able for multiplication. (Bj.) 64 



VII. By repetition. (Bj.) 67 



VIII. Restraint of environment causing suppression of 



structures. (Cj.) 70 



IX. Mechanical restraint. (C..) 77 



X. Disuse. (C3, D2.) 80 



XL Intrinsic suppression of structures and functions. 



(Di-) 86 



