PREFACE. 



THE object of the writer of the present work has been 

 twofold ; first, to lay before the Naturalist a complete view 

 of the organization and physiological relations of every 

 class of living beings ; and secondly, to offer to the Ana- 

 tomical Student a succinct account of the structure and 

 developement of the vital organs through all the modifi- 

 cations that they present in the long series of the animal 

 creation. 



Extensive indeed is the field of study that offers itself 

 to the zealous cultivator of Natural History, if he would 

 step beyond the limits that not unfrequently too narrowly 

 circumscribe his views of animated nature. Needlessly 

 to multiply specific distinctions, or to arrange trivial groups 

 of external forms in imaginary circles, is an easy occupa- 

 tion to the superficial Zoologist, easier perhaps than it 

 would be to one more deeply conversant with the anato- 

 my and intimate composition of the creatures thus sum- 

 marily classified; and, accordingly, it is by no means un- 

 common in the present day to see the most strenuous 

 supporters of this or that theory resolutely shutting their 

 eyes against all evidence deducible from the laws of phy- 

 siology, and stoutly maintaining that outward form is in 

 itself enough for the purpose they have in view, namely, 

 the establishment of some favourite principle or fancied 



