204 



In all animals the minute structure of the brain, as detected by the 

 microscope, appears in a measure similar, consisting of globules, and 

 a more or less fluid and often elastic transparent matter. The gan- 

 glions appear also similarly composed in all the animal tribes of a 

 congeries of nervous fibres. 



Some Observations on the Migration of Birds. By the late Edward 

 Jenner, M.D. F.R.S. ; with an Introductory Letter to Sir Humphry 

 Davy, Bart. P.R.S. By the Rev. G. C. Jenner. Read November 

 27, 1823. [Phil. Trans. 1824, p. 11.] 



The author's intention in this paper is not to give a general history 

 of the migration of birds, but to adduce some hitherto unnoticed facts 

 respecting the causes which excite the bird at certain seasons of the 

 year to quit one country for another. Among these the most pro- 

 minent are certain changes in the generative organs, and the neces- 

 sity of a climate or country where they can be better accommodated 

 with succours for their infant brood than in that from which they de- 

 part. He also adduces facts to prove that their departure from this 

 country is not in consequence of change of temperature or scarcity 

 of food, but the result of the accomplishment of their errand, namely, 

 the incubation and rearing their young. 



The authbr then offers some remarks on the winter birds of pas- 

 sage, tending to show that they quit this country in spring in quest 

 of a situation better adapted to their intended purpose, and that they 

 are actuated by the same impulse in leaving this country that causes 

 the spring birds to come to it, and not by want of food. That the 

 emigration of the winter birds is less complete than that of the spring 

 migrators, and that some species, especially the wild duck and wood- 

 pigeon, breed here. 



Redwings and fieldfares appear to be the most regular and uniform 

 in their appearance and disappearance, and never seem to risk the 

 trial of incubation here. 



Dr. Jenner remarks, that in severe and long- continued frosts, birds 

 often quit the country through want of food, but that they return 

 upon the approach of more temperate weather, which is announced 

 by their reappearance. The arrival of water birds, on the contrary, 

 forebodes the approach of intense frost. 



The author then offers some observations on the singing of birds, 

 and details some additional facts and particulars respecting the dif- 

 ferent sizes of the generative organs of birds, as they appear at dif- 

 ferent seasons of the year. 



On the Nature of the Acid and Saline Matters usually existing in the 

 Stomachs of Animals. By William Prout, M.D. F.R.S. Read 

 December 11, 1823. [PA*7. Trans. 1824, p. 45.] 



The object of this communication is to prove that the free acid 

 usually existing in the stomachs of animals is the muriatic acid, and 

 that the salts present are alkaline muriates. 



