No. I.] THE VERTEBRATE EAR. jg/ 



endanger the life of the animal. Hoffmann's account of the 

 differentiation of the ear sac is in harmony with the prevailing 

 ideas, that the sac first divides into superior and inferior por- 

 tions before the former gives rise to the canals and the adult 

 utriculus, while the latter is converted into the adult sacculus 

 (receiving the endolymphatic duct) and the cochlear tube. For 

 his account of the development of the semicircular canals, he 

 quotes Rathke's observations and applies them to Lacerta. The 

 sensory epithelium soon makes its appearance by the growth 

 in length of its cells and the formation of sensory hairs on the 

 hair cells, and the distinction between sensory and non-sensory 

 areas is still further increased by the flattening of the cells of 

 the latter. 



In respect to the nerve-end organs, he says (p. 2015) : "Da- 

 durch, dass das Gehohrblaschen sich in die verschiedenen Ab- 

 theilungen sondert, wird auch das Hohrepithel in eben so viele 

 einzelne Flecke zerlegt, zu denen sich dann der Nervus acusti- 

 cus begiebt. Das Hohrepithel zerfallt mithin bekanntlich in : 

 i) Eine Macula acustica recessus utriculi ; 2) eine Macula acus- 

 tica sacculi ; 3) eine Macula s. papilla acustica basilaris ; 4) eine 

 Macula s. papilla acustica lagenas ; 5) eine Macula acustica neg- 

 lecta ; 6, 7, 8) drei Macule s. cristas acusticae ampullarum." 



Development in the Birds. 



Although so many authors have studied the embryology of 

 the Chick, no one seems to have followed the development of 

 its auditory organ beyond the very earliest stage, and there are 

 no observations known to me on the division of its sense organs. 

 I have seen the sense organ which is invaginated before it has 

 gone below the surface and while still in the saucer stage, but 

 further than this I have not followed its development. His^ 

 {loc. cit. p. 107) says: "Jede Gehorblase erscheint als eine dem 

 Nachhirn seitlich anliegende Grube, welche nach innen, nach 

 vorn und nach hinten von einer scharfen, doppelten Contour 

 umsaurht ist, wahrend die aussere Granze in unbestimmter 

 Weise sich in die Seitenwande des Kopfes verliert. Ihr 

 durchmesser betragt zu der Zeit ca. o. i mm. Etwas friiher 

 sieht man in der Flachenansicht nur einen vierseitigen Flecken 



1 Untersuch. te. d. Erste Anlage dei' Wirhelthierslcibes. Leipzig, 1 868. 



