VI. INTKODUCTION. 



that, throughout the enth-e Collection, such a group should 

 be segregated, so as to form the unit of the series. Eventu- 

 ally, in order that the sketches, which it was proposed to 

 print for that purpose on tablets, might all be in positions 

 where they could conveniently be read, it was found to be 

 expedient that each group or unit should occupy an equal 

 space ; and as the blocks on which the table cases rested 

 were to be fitted up with trays or drawers, twelve of which 

 would occupy the table case without loss of room, these trays 

 or drawers were adopted as the receptacles and boundaries of 

 the groups. 



The drawers measured 27 inches in length by 16 inches 

 in breadth, and their number in the twenty table cases when 

 completed would be 240. Then arose the problem how best 

 to divide the 28 classes of Invertebrate Animals into 240 

 groups, each of which should be capable of affording mate- 

 rials for a biological notice, such as might be read with 

 interest by any intelligent visitor. 



The entire plan of the table cases, and the limits of many 

 of the groups, were committed to writing before any consider- 

 able advance had been made in procuring specimens. In 

 one respect this circumstance was found to be very advan- 

 tageous — our desiderata were at once well defined. It was 

 an object that each of the groups should be illustrated by 

 carefully-selected specimens ; and until this could be attained, 

 other acquisitions need not be sought for. In making 

 purchases, such an object, steadily kept in view, exercises a 

 powerful influence against the seductive attractions of "great 

 bargains," which often turn out to be great misfortunes to a 

 museum. Moreover, in accepting donations, it is sometimes 

 convenient to be able to refer to a fixed plan. Where room 

 is scanty, as in most museums, nothing is more subversive of 

 order, or more fatal to an instructive arrangement, than the 



