Oct. 8, 1874] 



NATURE 



Afi'J 



by a Roman 2, whilst its abnormal state is indicated by 

 the same figure in italics. The relative positions of the 

 four different anatomical facts is retained throughout : — 



(1) PaL.'EORNITHIN.'E 



(2) stringopin.e . 



(3) Arim.e . . . 



(4) pvrrhurin/e . 



(5) Pl.ATYCERIN.E . 



(6) Chrysotin-t; 



+ 



On this arrangement, the Lories, belonging to \htPahT- 



ornilliiiKT, their zoological formula is 2 h + > whilst 



that of Cyanoiiini'ip/u/s, which is one of the PlatyforiinT, 

 is .? — — +• By this means the relations of the dif- 

 ferent groups to one another are readily recognisable. 



Next, in the attempt to arrive at a correct detailed 

 classification, the question as to the zoological formula of 

 the ancestral Psittacine form must be one of primary 

 importance. This can only be arrived at by a comparison 

 of the other bird-types with that of the parrots. Taking 

 the characters employed in Table I., and similarly formu- 

 lating such birds as the fowl, duck, rail, stork, and 

 cuckoo, they all agree in being represented by 2 -j- + + ( i ) ; 

 others, like the kingfishers and hornbills, have the for- 

 mula 2 1- + (2) ; whilst a third type, with only a left 



carotid, are included in the L - -}- -j- type (3). No others 

 of importance exist. Fronr which of them did that of the 

 Psittaci spring? It must have been from one; and, 

 peculiarly enough, there are genera to be found among 

 them which closely approach all three, for— 



The formula of Pittacus is 3 -\ — | — |- 



,, „ Palaoniis „ 2 j — j- 



„ ,, Cacafi/a „ L — -| — j- 



However, this only shows that the sub-order is a very 

 ancient one, and has undergone changes analogous to the 

 ' whole class Avcs, and it does not complicate the problem 

 ' in the least. 



There are parrots with two normal carotids, e.^. the 

 ' PalceoynithincE ; there are others in which the ambiens is 

 ' present, e.g. the Arince ; most have a furcula and also an 

 , oil-gland. 



Now suppose that when steam-engines were first intro- 

 duced they had all been constructed with steam-whistles 

 attached. Suppose that shortly afterwards several had 

 ( been exported to different colonies, and that ever after- 

 I wards each colony had, with the originals as patterns, 

 gone on constructing them for their own use, improving 

 upon the original design as they thought best. Suppose 

 j that by certain individual manufacturers a gong was sub- 

 I stituted for the whistle ; in others a bell, and in a third 

 no sounding apparatus at all. A traveller going through 

 I the different countries at the present time would probably 

 I find whistle-engines wherever he went, though in different 

 places gongs or bells will have replaced the whistle. 

 Knowing nothing about the history of the steam-engine, 

 is he not justified in inferring that it was originally con- 

 structed with a whistle ; for otherwise would it be likely 

 that each colony should have independently employed the 

 same method of signalling, when there were several to be 

 chosen from .' 



The naturalist, similarly, as an uninitiated looker-on at 

 the contrivances of nature, finds the same type of struc- 

 ture running through forms not very intimately allied ; 

 as, for example, two symmetrical carotids, in reptiles, 

 mammals, and some birds ; or an ambiens muscle in the 

 fowl, the eagle, the cuckoo, and the plantain-cutter. 

 When, therelore, these fundamental arrangements are 

 found to exist (though perhaps not combined in any one 

 individual) in any well-defined group like the parrots, may 

 it not be legitimately inferred that the ancestor of that 



group possessed them in their full and unmodified form ? 

 Undoubtedly it may ; and on this principle we can almost 

 certainly assume that the ancestral parrot possessed two 

 normal carotids, an ambiens muscle, a complete furcula, 

 and an oil-gland; in fact, that its formula was 2 -| — | — h; 

 and that all those species in which one or other of the 

 included characters differ from this type formula, they do 

 so on account of forces having modified the ancestral 

 form. This line of argument therefore leads us to infer 

 the extinction of the earliest form of parrot, unless some 

 yet undissected genus is subsequently found to correspond 

 with it ; and all the existing genera must be referred to 

 collateral branches, in which at least one operation of 

 modification has been accomplished. Those which have 

 undergone no further change from the 2 -j — | — f- type are 



the Palffoniitliina (2 f- +), and the Ariiia (2 -\- -\- -j-). 



Now the question presents itself, are all those with the 

 modified carotid {3), members of a single stem, and those 

 with the unmodified carotid (2) members of another, 

 similar losses having occurred in both to develop the 

 subjoined series .' 



Table IT. 



2 - + + .? + + + 



2 - - -f 2 - + + 



L- + - 2- - + 



2- + - 

 Or must those types be blended in which the formulas 

 correspond, irrespective of the carotids ? My placing the 

 carotid index first expresses my belief as to its primary 

 importance ; and this is because the conformation it re- 

 presents is extremely peculiar and unique among birds, 

 and is therefore less likely to have appeared except as the 

 operation of a specially applied force on a single collec- 

 tion of individuals, the power of transmission being in- 

 herited. From this it may be inferred that the ancestral 

 unmodified stem shortly sent oft" a branch represented b' 

 2 -\- -\ — \-, which persists as such in the Ariiia. The main 

 stem and its branch must each have, before long, had a 



branch of its own, represented by 2 \ — |- and 2 1 — |-, 



which persist as the Palaornitliina: and the Pyrrhurina. 



From the 2 h + division sprang the 2 1- {Striiigo- 



piiuT), and the genus Cacatua (L - -j — ), as did the 



2 — 1- {Platyct'rciiUT) and the 2 1- - (C/irysolince) 



from the 2 1 — |- division. The genus Cacatua is pecu- 

 liar in having only the left carotid running normally, it 

 must therefore be connected with the normal 2 carotid 

 stem, and many Cacatinmr;, like the Cockateel and the 

 Banksian Cockatoo, are represented by the formula 

 2 - -\ — |-. Some of the true Cockatoos, and some only, 

 have no oil-gland. 



My object in giving this somewhat lengthy illustration 

 on the present occasion is to show how much facility a 

 method of formulation affords in the working out of a 

 minor problem of the great doctrine of heredity, such as 

 the classification of the parrots. It makes comparison 

 easy, it facilitates the performance of operations of addi- 

 tion and subtraction, bringing all the stages of the process 

 before the mind's eye without any mental effort. Is it 

 not one to be further developed ? 



THE OPTICS OF THE SPECTROSCOPE 



NOW that the Spectroscope is becoming an instrument 

 of world-wide use, we think it will be not unin- 

 teresting to call attention to some few points that appear 

 to be often overlooked in designing the instrument for 

 various purposes ; and in order to ascertain the best 

 arrangement, we cannot do better than analyse the effects 

 produced in any spectroscope by varying the proportion 

 of its parts. We must, however, premise by saying that 

 the power of an instrument is not altogether dependent 

 on the dispersive power of the prisms, but also on the 

 width of the imigc of the slit in the eyepiece of the tele- 



