INTRODUCTION. XVll. 



and another, and between successive groups of forms, that 

 constitutes the chief function of a museum. 



In reporting the progress of a work which has found 

 employment for me more or less constantly during a period of 

 twelve or thirteen years, it is a gratifying duty to acknowledge 

 the assistance afforded me from many quarters. An impulse 

 highly favourable to the success of the plan was given at the 

 outset, by the provision of a series of table cases such as I 

 have not seen surpassed elsewhere. This has been seconded 

 by the purchase from time to time of many valuable works on 

 biology, chiefly Continental, and such as are rarely to be 

 found in provincial libraries, though almost indispensable for 

 the study of special classes of the Invertebrata. Liberal con- 

 sideration has, moreover, always been given to the acquisition, 

 by purchase or otherwise, of specimens necessary for the 

 Collection. Acknowledgments are also due to the Chairman 

 and Members of the Museum Committee, not only for the 

 honour of a place at their board, but also for the sympathy 

 and support which have rendered the meetings of the Com- 

 mittee occasions to myself of much gratification. 



To Mr. Moore, the Curator of the Museum, I am indebted 

 for many valuable suggestions, especially for the very import- 

 ant recommendation through which the series has been made 

 an ascending instead of a descending one. The Echinoder- 

 mata chiefly, and the Crustacea almost entirely, were obtained 

 for the Museum through Mr. Moore. Nearly the whole of 

 Echinoidea were named by Professor Alexander Agassiz, 

 on one of his visits to the Museum ; and it was only in the 

 course of naming and arranging the rest of the Echinoder- 

 mata and the Crustacea that the care and discrimination 

 shown by Mr. Moore in the selection of the specimens 

 became fully known to me. One very valuable class of acqui- 

 sitions, those collected and presented by Masters of merchant 



