PREFACE. 



gratification to be derived tVoni the study of this braneli of 

 natural history, of which the present work bears such ample 

 testimony. P'or a long series of years, the collection of materials 

 for its completion has been a ceaseless labour of love. Indeed, 

 had it not been thus, it would have been impossible for me to 

 liave proceeded in an undertaking " of which the profit, if by 

 great chance there should be any, could not be expected to 

 repay, even the cost of books required in it, and from which any 

 fame must necessarily be confined to a very limited circle*," 

 and in which the time absorbed in the preparation of the text, 

 and in microscopically dissecting so many minute objects re- 

 presented in the wood-cuts, has been so great. I have, however, 

 persevered, and, if I shall have succeeded in inducing any of my 

 readers to pursue the science with a higher aim than that of 

 collecting specimens, by investigating the habits and the corre- 

 sponding organisation of these animals with a view to the dis- 

 covery of their natural relations and classification, my labours 

 will not have been in vain. 



* Kirby and Speiice, Introd, pref. vol. i. p. 10. 



