INTRODUCTION. 7 



We maintain that this new light should be reflected in 

 our museums, especially in our Synoptic Collections ; that 

 here the workings of the law of heredity by which ani- 

 mals are bound together by blood relationship should be 

 illustrated by specimens, drawings, models, by everything 

 in brief, that can most strongly impress the student. This 

 demonstration would be more effective had we a closer 

 acquaintance with the ancestral fauna of pre-Cambrian and 

 Cambrian times. The masterly researches of Walcott into 

 the Cambrian and Lower Silurian rocks, and the invalu- 

 able investigations of Matthews in the Cambrian forma- 

 tions of New Brunswick prove how important are these 

 sources for studies in evolution in a field hitherto almost 

 unexplored. 



Other terms which do not appear in this Guide are 

 "degraded," "degenerate," "retrogressive," and "worm" 

 as applied to the caterpillar stage of the Lepidoptera. 



The first two, "degraded" and "degenerate," are not 

 used for two reasons : first, because they are associated 

 in the popular mind with moral considerations, and this 

 association often leads to mental confusion; secondly, 

 because we cannot see why an animal that has developed 

 a part or an organ to the immense advantage of itself and 

 its race should be called "degraded," even though many 

 other organs have fallen into disuse or wholly disappeared 

 in the process. In the case of parasites the use of these 

 terms might be more allowable, were it not for the first 

 reason stated. 



The word "retrogressive" is not used because it is mis- 

 leading, since animals do not in reality go back to a more 

 primitive and generalized condition, however much they 

 may appear to do so. This is proved by the position of 

 the so called "retrogressive species" in a genealogical 

 record which can never be among the ancestral trunk 

 forms. It cannot be, because these species as a rule bear 

 evidences of the evolutionary stages through which they 

 have passed ; and where such evidences are not apparent 



