iv. INTEODTJCTION. 



tage. The classes of invertebrate animals cannot well be 

 represented in a single ascending or descending series. 

 Probably it would not be possible on any symmetrical plan 

 to assign to them their proper positions relatively to each 

 other : but some palpable incongruities might be avoided 

 by the use of table-cases on a ground-plan resembling a 

 genealogical tree, one proposed form of which is represented 

 by a diagram in a work published by Professor Rolleston. 

 (See opposite page.) 



The importance of a suitable ground-plan for cases in 

 museums seems to be much under-rated. "When a class of 

 students visit a museum frequently, the localities of cases 

 containing special groups become indelibly impressed upon 

 the memory. This might be turned to good account. 



In preparing the first scheme of the collection, it seemed 

 essential that plain and moderately simple printed descrip- 

 tions of the life history of the animals should accompany 

 the specimens : therefore, as it was clearly impossible to 

 describe every genus, it became necessary to fix on some 

 mode of associating in groups a number of examples to which 

 the descriptions might apply. Such divisions as ''classes" 

 and "orders" were manifestly too large ; whilst "families" 

 varied from a single genus, including a solitary species, to an 

 army of more than a thousand genera, — e. g., the Linnoean 

 families Geramhycidce and CurcuUonida in the Coleoptera. 

 It was with some regret that the idea of attaching a readable 

 sketch to each division of a given rank in recent systems, of 

 classification was relinquished, but it was found to be imprac- 

 ticable ; and the life history sketch thus became the founda- 

 tion of the arrangement eventually adopted. 



Whether it might be a few species, or a genus, or a 

 family, or an order, that seemed to afford suitable scope for 

 a page of readable and instructive matter, it was decided 



