172 FOURTH REPORT — 1834. 



other observers*, is perhaps too much within the province of 

 pure animal physiology to require notice here. The laws, how- 

 ever, which i-egulate the assumption and changes of plumage are 

 of the utmost consequence for the exact discrimination of species. 

 These laws have received great attention from Mr. Yarrell, who 

 has lately added one to those previously establishedf, viz. that 

 " Whenever adult birds assume a plumage durmg the breeding- 

 season decidedly different in colour from that ivliich they bear in 

 the wilder, the young have a plumage intermediate in the gene- 

 ral tone of its colour compared with the tivo periodical states of 

 the parent birds, and bearing also indications of the colours to be 

 afterwards attained at either period." In the same paper Mr. 

 Yarrell has stated some experiments, the results of which fully 

 establish the point that in many cases a change of plumage is 

 certainly occasioned by a change of colour in the feather itself J, 

 quite independently of moulting. 



The difficulty of finding specific characters for birds which 

 shall be applicable to both sexes and all ages, particularly in 

 those groups in which the changes of plumage above alluded to 

 are most prevalent, has been severely felt by ornithologists. Mr. 

 Macgillivray has considered this subject in a paper published in 

 the 4th volume of the Wernerian Memoirs^. He has pointed 

 out the insufficiency of some of those in common use, particu- 

 larly such as are derived from coloiu". He thinks it would be 

 possible to obtain others, from the situation, form, and position 

 of the feathers, which would be more preferable, as being of 

 general application and founded upon permanent and essential 

 organs. Mr. Macgillivray has annexed, as examples, the cha- 

 racters of several species drawn up in this manner. His sug- 

 gestions deserve to be considered, although it may be questioned 

 whether such characters will be foimd " sufficiently diversified " 

 to admit of being adopted in all cases. 



3. Repttilia, Cuv. — The study of the animals belonging to 

 this division of the Vertebrata is difficult, and has received far 

 less attention from naturalists than that of either of the preced- 

 ing classes. Hence we are at present but little advanced in the 

 details of their natural arrangement. The propi'iety of separat- 

 ing off the Amphibia, and considering these last as a distinct 

 class, is becoming every day more generally acknowledged. This 

 separation was first proposed by Latreille || so long ago as in 



• See more particularly Macgillivray in Ed'inh. Netv Phil. Joitrn. 1827. 



f Zool. Irans., vol. i. p. 13. 



X This had been often suspected to be the case, (see Whitear in Linn. Trans., 

 vol. xii. p. 524, and Fleming in Edinh. Phil. Journ.,\o\. ii. p. 271,) but never 

 before ascertained by direct experiment. 



§ p. 517. II Nouv. Diet. d'Hisi. Nat., 1st edition. 



