30 AYERS. [Vol. VI. 



municate directly with the utriculus, while the posterior two- 

 thirds communicate with the sacculus. The walls of this evag- 

 ination do not show a continuation of the utriculo-saccular par- 

 tition, as Ketel (i6o, 1872) and Retzius (237, 1881) have main- 

 tained and as it appears at first glance, for a careful study of the 

 partition shows that it exists on the floor of the ear as a low 

 fold, and that it is pushed cephalad by the lagena to such an 

 extent as to mask the true position of this chamber. The re- 

 cessus utriculi lies cephalad of the partition and forms a depres- 

 sion in the floor of the utriculus. 



The canals, their ampullae trifidae, and the endolymphatic 

 ducts offer exceptional features ; but as I shall describe them 

 more fully in another paper, they need not detain us here. The 

 sense organs included in the Petromyzon ear are seven in num- 

 ber: the maculae utriculi and sacculi, each discreet sensory 

 patches, the cristae acusticas ampullarum anteriores et posteri- 

 ores, also discreet, and the papilla lagenas, which is possibly 

 continuous with the macula utriculi, the sense organ in the 

 recessus utriculi, and the sense organ of the undeveloped ex- 

 ternal ampulla, about which we need more information. 



Beginning with the macula utriculi anteriorly, we find this 

 sense organ placed anterior to the plane of the utriculo-saccular 

 partition. It passes over the anterior edge of the sacculo- 

 lagenar pocket, down its anterior wall, and out over its floor 

 for a short distance. It does not reach to the base of the hill 

 which lies in the bottom of the saccular portion of the pocket 

 {i.e. the lagena). Its epithelium passes out into the columnar 

 lining of the pocket, and this, in its turn, soon increases in 

 height and becomes columnar as it ascends the hill, or papilla 

 lagenae. The epithelium on the posterior face of the papilla 

 does not change again, but is continuous, with at most only an 

 indication of a break, with the macula sacculi. 



Minius polyglottiis (compare Cut 10). 



The utriculus of the Mocking-bird is relatively very small, 

 and is somewhat tubular, that portion of it containing the 

 macula utriculi being marked off from the more central portion 

 by a constriction of the walls of this chamber, followed by an 

 enlargement, the chamber of the recessus utriculi, which is 

 somewhat flattened from above downwards. It has a reniform 



