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, B3.) .... 47 



III. Secondarily as a means of protection and offence. 



(A3, B4.) 52 



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

 v. Secondarily from mimetic influences. (Aj, B,.). 60 



VI. Prolonged development under conditions favor- 

 able for multiplication. (Bj.) .... 64 



VII. By repetition. (B3.) ^ . 67 



VIII. Restraint of environment causing suppression of 



structures. (Ci.) .... . . .70 



IX. Mechanical restraint. (Cj.) .77 



X. Disuse. (C3, Dj.) 80 



XI. Intrinsic suppression of structures and functions. 



(D,.) 86 



