412 DR. J, MTJRIE ON THE EMU. [Apr. 1 1 , 



lungs, without being necessitated to allow it to escape, in order to 

 perform the act of inspiration" (ibid. pp. 136-139). 



Wedemeyer was inclined to regard it as an air-reservoir for oxy- 

 genizing the blood, as did Fremery. 



Meckel, in summing up the opinions of these authors, gives his 

 own to this eflFect : — That it has no connexion with the voice, that 

 more probably it facilitates running, and that in exceptional cir- 

 cumstances it may functionally answer as a swimming-bladder. 



Dr. Macartney advances the idea that " the peculiar sound be- 

 longing to the New Holland Ostrich is entirely occasioned by the 

 reverberation or resonance produced in the membranous bag con- 

 nected with the front of the trachea," giving analogous instances in 

 the bird, horse, howling-baboon, and bull-frog. 



Professor Owen, as already mentioned, at least considers there is 

 an existing relation between the sac and the sound. Dr. George 

 Bennett* states, " the only sound emitted by the Emeu is a sort of 

 hollow booming note. It is considered to be produced in the female 

 by means of the expansion and contraction of a large membranous bag 

 surrounding an oblong opening through the rings of the trachea." 



Mr. Bartlett, Superintendent of the Society's Gardens, has made 

 many observations on the voices and habits of the Struthious Birds 

 living in the Society's Menagerie. 



On discussing the mooted question of the use of the sac with him, 

 he supplies me with the following information : — " I have no reason 

 to believe the sac and opening in the trachea in the Emu have any- 

 thing whatever to do with swimming, breathing, or running, but I 

 consider them as constituting simply the organ of sound employed 

 by both male and female during the breeding-season. Probably at 

 other times the sound produced by the female is louder and of a 

 more regular drumming kind than in the male bird, also the lower 

 part of the neck is inflated to a much greater extent in the female 

 than in the male during the time these sounds are emitted. I am, 

 moreover, unable to say whether the cavity is larger in the female 

 than in the male." 



In offering my own opinion upon the supposed function of this 

 very remarkable tracheal appendage, unknown in any other species 

 of bird, I must confess myself very undecided concerning its adap- 

 tation to one special use. Placing the opinions of the several au- 

 thorities in a tabular form they may be stated as follows : — 



1st. Respiratory purposes (oxygenation of the blood). 



2nd. As a swimming-bladder. 



3rd. As an air-reservoir in running. 



4th. For simple vocal resonance. 



5th. Sexual organ of sound during the breeding-season. 



With respect to the first of these assigned functions, this may be 

 looked at in a twofold view. The sac may either be regarded as a 

 membranous expanse, the vascularity of which permits it to deoxy- 

 genize the inspired air, as does the lung ; or it may merely supply 

 the place of an air-reservoir to the lungs themselves. The first of 

 * Gatlierings of a Naturalist in Australia (London, 1860), p. 219. 



