PREFACE. Vll 



his object having been simply to make use of such expres- 

 sions as seemed best fitted to convey his meaning. If, as he 

 has some reason to fear, his anxiety for this, and his wish to 

 present the subject in different points of view, have led him 

 into needless repetitions, he can only now express his regret 

 that circumstances latterly have not allowed him leisure to 

 determine what might be retrenched with advantage. 



In explanation of the absence in the text of any reference 

 to the accompanying Plates, it is but fair to mention that 

 their introduction was an after- thought. The difficulties in 

 the way of publication interfered with the illustration of the 

 text by wood-cuts, as is now commonly done in treatises of 

 this kind, and it was not till after the work was in print 

 that the use of outline figures was suggested. Much selec- 

 tion was then impossible, but the Author hopes that those 

 which have been introduced will be found an advantage, from 

 the acknowledged importance of illustrative figures of some 

 kind, when frequent reference has to be made to peculiarities 

 of structure and conformation. 



To personal researches on the subject in hand the Author 

 cannot make much pretension ; he can claim little more than 

 to have taken for many years a lively interest in the observa- 

 tions of others. He must, therefore, readily admit his liability 

 to- fallacies and misconception in making his statements at 

 second hand, though there may be some compensation for 

 this in a comparative freedom from influences which are apt 

 to bias the views of original observers. He may at least, in all 

 honesty, claim to have entered on the consideration of the 

 question without any conscious prepossession one way or 



