INTRODUCTION. vii. 



gift of a collection, coupled with a stipulation that it must be 

 displayed in some special way. It is far better to forego the 

 possession even of a valuable series of specimens, than to 

 sacrifice order for their sake. 



The number of groups, 240, will no doubt appear to have 

 been determined simply as a matter of convenience. To a 

 certain extent this is true. It is also true that after a careful 

 reference to the best accessible authorities on each of the 

 Invertebrate Classes, in which much assistance was afforded 

 me by the many valuable scientific works in the Free Public 

 Library of Liverpool, it seemed probable that most of the 

 prominent forms in all the classes might be exhibited in 

 pairs, with their names and localities attached in large and 

 legible characters, in an area less than 1,000 square feet ; 

 and that they might conveniently be disposed in 240 groups, 

 occupying twenty table cases. For these the suite of rooms 

 above referred to afforded ample accommodation. 



Four table cases contain the Protozoa and the C(ELEn- 

 TERATA. Seven are given to the Molluscoida and MoL- 

 LUSCA. Two are occupied by the sub-kingdom Annuloida, 

 including Echinodermata and Scolecida. Three are given 

 to Annelida and Crustacea. Four cases hold the Myria- 

 PODA, Arachnida, and Insecta. For constant exhibition to 

 the public the series as thus constituted may be regarded as 

 quite sufficiently extensive. 



It is hardly necessary for me to point out the difficulties 

 and disadvantages which must arise in the course of an 

 attempt to form a collection in which the whole of the inver- 

 tebrate classes are divided into a given number of equal 

 groups. If all very distinct forms are to be exhibited, some 

 groups must be heterogeneous in composition, but not neces- 

 sarily very many. Such forms as Pycnogonum, Forjicula, 

 and Sagitta may have to appear as associated with other not 



