130 EMBRYOLOGY OF TTIK LOWER VERTEBRATES CH. 



s.e 



se. 



shadows the anterior vertical semicircular canal (a.v) and a little 

 later a similar bulging more ventral in position the horizontal 

 canal (h.c). The lagena also is foreshadowed by a slight downward 

 bulging of the floor of the otocyst. 



\Vith further development 'the posterior vertical canal rudiment 



appears also as a bulg- 

 ing of the otocyst wall 

 continuous with that 

 which will form the 

 anterior canal (Fiir. 7_. 

 C-F, p.v). The three 

 canal rudiments come 

 .to project more and 

 more prominently, the 

 recess assumes the 

 tubular shape of the 

 endolymphatic duct 

 and the lower portion 

 of the otocyst (saccule) 

 with * its projecting 

 lagenar pocket and en- 

 dolymphatic duct be- 

 comes more sharply 

 marked off from the rest 

 of the otocyst (utricle). 

 The pouch -like rudi- 

 ments of the semicir- 

 cular canals, as they 

 V" ^^ come to project more 

 freely from the utricle, 

 assume a flattened form 

 and finally the central 



FJ;. 72. Illustrating the development of the otocyst in the portion of the wall on 

 Koul. (A-G after Rothig and Brugsch, 1902 ; H after Q^Q^ side billies in- 

 Retzius.) , i '"" 



wards and fuses with 

 that on the other. 



In this way the 



central portion of the 

 cavity of each pouch 

 becomes obliterated 

 while the persisting 



peripheral part takes the form of a, curved tube the definitive canal. 

 At lirst the space sublended by the canal is traversed bv a continu- 

 ous Heptuni formed out of the fused walls but this soon disappears 

 leaving the canal Bfl a freely projecting arch which opens into the 

 utriel- h end. The ampulla appears at an early stage as a 



dilatation of the canal rudiment at one end. 



will already have been gathered, the three canal rudiments do 



A and H, early slaves; C. towards '-nd ot si-vcntli day; D, to- 

 wards cud ot fi-litli day; E, fivo days ; F, tmvants cud of ninth 

 !n\\;iids end of twelfth day; H, adult. A is a view CM mi 

 in front, 15 from In-hind, while C-H represent the left otocyst as 

 seen from the left side. .c, antci ior vertical canal ; It.c, horizontal 

 canal; l<tg, lagena: //.<, pfjsterior vertical canal; r, recess; s.e, 

 endolymphatic dm-t. 



