Vlll PREFACE. 



phenomena, pointing out what they shew and what they do not 

 shew, having regard always to deficiencies in the evidence. 



That this is a dangerous course I am aware. But in any 

 discussion of a problem in the light of insufficient knowledge the 

 real danger is not that a particular conclusion may be wrong, for 

 that is a transient fault, but rather that the facts themselves may 

 be so distorted as to be valueless to others when the conclusions 

 that they were used to shew have been discarded. This danger I 

 have sought indifferently to avoid by printing the facts as far as 

 possible apart from all comment, knowing well how temporary the 

 worth of these comments is likely to be. I have thus tried to 

 avoid general statements and have kept the descriptions to 

 particular cases, unless the number of similar cases is great and 

 an inclusive description is enough. 



Each separate paragraph relating a fact has been as far as 

 possible isolated and made to stand alone ; so that if any one may 

 hereafter care to go on with the work he will be able to cut out 

 the discarded comments and rearrange the facts in any order 

 preferred, inserting new facts as they come to hand. Most of 

 these facts are numbered for reference. The numbers are distrib- 

 uted on no strict system, but are put in where likely to be useful. 



For almost every fact stated or mentioned one reference at least 

 is given. When this is not the case the fact is either notorious, 

 or else the result of my own observation. In collecting evidence I 

 have freely used the collections of former writers, especially those 

 of Geoffroy St Hilaire, Ahlfeld, and Wenzel Gruber, but unless 

 the contrary is stated, each passage referred to has been seen in 

 its original place. By this system I hope I have avoided evidence 

 corrupted by repetition. Several well known conceptions, notably 

 that of the presence of order in abnormality, first formulated by 

 Isidore Geoffroy St Hilaire, have been developed and exhibited 

 in their relation to recent views. 



The professed morphologist will note that many of the state- 

 ments are made on authority unfamiliar to him. I have spared no 

 pains to verify the facts wherever possible, and no case has been 

 admitted without remark if there was reason to doubt its authen- 

 ticity. So long as skilled zoologists continue to neglect all forms 

 that are abnormal the student of Variation must turn to other 

 sources. 



This neglect of the Study of Variation may be attributed in 



