236 FISSIROSTRAL SUBORDER ©F 



elongation of beak, each amongst its own allies representing the 

 Tenuirostral tendency. I have already explained my view of Trogon- 

 idse as in some striking points approaching Musophagidse, and having 

 well marked the characters of our new sub-order, yet by their power 

 of flight, their feeding on the wing, and their peculiar plumage, 

 sufficiently showing their Fissirostral tendency. 



In Mr. Wallace's valuable paper on the natural arrangement of 

 birds, which contains his suggestions respecting the Fissirostral and 

 Scansorial groups, betakes occasion to make an attack on the system 

 of definite numbers in nature, to which I shall take the present 

 opportunity of offering some reply, since, though he immediately 

 refers to Mr. Swainson's system, his arguments, granting their suf- 

 ficiency, would undoubtedly apply to all schemes which suppose 

 definite tendencies as to number. I might, perhaps, not improperly 

 begin by observing that definite numbers of parts in certain series of 

 organisms being indubitable facts, and yet being fully exposed to one 

 of Mr. "Wallace's objections — setting bounds to the variety of Nature 

 - — ^we must receive the fact in preference to a theory, and it perhaps 

 seems to us quite as certain a fact, that the best arrangements in 

 Natural History always show a tendency to the recurrence of the 

 same number of divisions of each great type which can only be 

 accounted for by its occurrence in Nature. Mr. "Wallace's first great 

 objection to definite numbers is thus stated by himself: — " Geologi- 

 cal investigations prove that the animals now existing in the earth 

 are probably not one-tenth, perhaps not one-hundredth, of those 

 which have existed ; for all before the tertiary epoch were of differ- 

 -ent species and mostly of different genera, and thousands of other 

 genera, families, and whole orders must have existed of which we 

 «re absolutely in ignorance- If therefore this regular system were 

 true of the whole, it must be quite imperceptible in the mere frag- 

 ment we have an acquaintance with. Instead of complete circles 

 being the rule, they should scarcely ever exist ; in fact the gaps left 

 in the system by its authors do not leave room enough for all the 

 forms that must have become extinct." Now we believe nobody 

 supposes that if we knew the whole animal creation, past as well as 

 present, we should find all types of structure developed to the same 

 extent, with the same number of families and sub-families, genera 

 and species ; and setting this notion aside as altogether preposterous, 

 what is it which is assumed by the advocates of definite number ? 

 It is just this, that under each distinct type of structure the minor 



