414 DR. J. MURIE ON THE EMU. [Apr. 11, 



the breeding- sea son, this seems a more reasonable one, inasmuch as 

 there are many instances of appearances and habits being temporarily 

 assumed in birds during the breeding-time — e. g. the wattles of the 

 Tragopan, and gular pouch of the Bustard &c. It agrees also with 

 the fact that inflation of the sac is more often noticed then, and the 

 peculiar drumming-noise is very frequent under sexual excitement. 



The phenomena accompanying distention of this tracheal pouch 

 in the birds in the Society's Gardens, as I have observed them, are 

 as follows : — The head and the neck are slightly raised, the latter 

 somewhat bent ; then there appears a swelling in the lower part of 

 the neck, and the bird with partly opened mouth gives utterance to 

 a series of grunting-like sounds, during which there is observable a 

 tremulous-like motion in the distended lower part of the neck, while 

 a certain compressed state of the glottis appears to take place. The 

 physiological action seems to be first a deep inspiration, followed by 

 expiration of a forced kind with total or partial closure of the glottis, 

 the tracheal pouch then fills, the aperture is more or less dilated, 

 and as the glottis is temporarily and successively relaxed the air 

 rushes from the lungs towards the open mouth, and, passing the 

 orifice of the sac in jets, gives rise to the peculiar hollow metallic 

 sounds, as does air when blown over the open bunghole of a cask. 



When an organ or ajipendage admits of so many ingenious sup- 

 positions as to its function as have been assigned to the one here 

 treated of, it is not surprising that the precise one should remain 

 uncertainly known. Interpreting the nature of the tracheal pouch 

 from structure and position, as well as the mode and times of its 

 being called into action, with the fact that the sac increases from 

 the young to the adult stage, and that its maximum of size and ap- 

 parent use correspond with the period of the procreative faculty, the 

 following seems to be its use : — that it serves as an organ of sound 

 employed by the bird under the phenomena incident to the passion 

 of lust, and hence is more powerfully brought into play during the 

 breeding-season. 



Homology . — It is not my intention in the present communication 

 to enter largely into the homology of this tracheal sac. Its wider 

 relations in a homological sense evidently possess as much of inter- 

 est as does the more limited study of its oeconomical function in the 

 Emu. I shall therefore only advert to the probable direction in 

 which its homology is to be studied, by referring to a note by the 

 French translators of Meckel's ' Vergleichende Anatomic,' " Ce sac 

 peut etre compare aux sacs laryngiens des sauriens, a raison de I'in- 

 fluence qu'exerce la volontc de I'animal sur la distention de cette 

 poche par I'air"*. Among Reptilians, however, the Chameleon, as 

 is well known, possesses a dilatable tracheal sac, in many respects 

 closely resembling that existing in the Emu. In a specimen of this 

 animal which I examined this pouch was of considerable size, and in 

 its textural structure quite like that of the Emu. Instead, however, 

 of being simple and ovoid or globular when distended, as iu the 

 Emu, it was pyriform, and with a partially constricted sacculus at 

 * Edition alieady cited, tome x. p. 405. 



