OF THE GALAPAGOS AECHIPELAGO. 469 



Jervis Island should also be visited, though they are little else but outlying rocks of 

 the larger islands, James and Indefatigable. 



Lastly, of unvisited islands there remain Wenman and Culpepper. The chance of 

 finding any land-birds on either of these rocks is exceedingly small ; but the fact of 

 their non-existence should be ascertained. 



All the islands that have already been investigated are vrorthy of further exploration. 

 The species of Mimus require more working out. Several of the so-called species of 

 Geospiza are but little known, such as G. magnirostris, G. ncbulosa, and G. dubia ; 

 also more specimens of Cactornis assimilis, C. abingdoni, and C. pallida are required to 

 complete our knowledge of these birds. 



Camarhynchus psittaculus and C. crassirostris are but little known, and still less 

 the bird described by Lafresnaye as C. cinereus. The two Herons (Butorides plumbea 

 and Nycticorax pauper) are as yet only known from immature birds ; more specimens 

 of the Flamingo would be useful, and a good series of the Petrels. Lastly, and 

 most important of all, a series of observations are required upon the attitude the 

 different species of Geospiza maintain towards one another, tending to show how far 

 the differences observable, or thought to be observable, in dried specimens indicate 

 the actual grouping in species of living individuals. 



From these remarks it will be seen that much useful work remains to be done in 

 these islands in the birds alone. In other branches of biological science even more 

 investigation is required. 



V. On the Vabiation of the Species in certain Geneea, and the consequent 

 Difficulty in defining Specific Limits. 



The acquisition of a large series of specimens of the different so-called species of 

 Geospiza renders the question as to the definiteness of the points of specific distinction 

 between them more diificult of solution than ever. Distinctions are plainly enough to 

 be seen between such birds as G. magnirosfris and G. parvula, where great disparity 

 in size is obvious. But these differences are gradually erased by almost insensible 

 steps by the interposition of G. strenua, G. fortis, and G. fuliginosa. The series 

 before me includes specimens that can almost as well be referred to either of two 

 contiguous species, so that their position can only be determined by assigning to each 

 species what must be called arbitrary standards of measurements of the bill alone. The 

 question follows. Do these birds, in their natural relations to one another, keep them- 

 selves to groups of individuals dependent upon the size of their bills ? The answer is 

 to be found rather by field-observation than by measuring skins. Were different 

 species, though closely allied, found to inhabit different islands, the case would be 

 much simplified. But what do we find ? Charles Island possesses three out of eight 

 so-called species, Chatham Island has no less than seven, James Island four, Indefati- 



