182 FRANCIS VILLY. 



Fig. 3. Similar section of an older embryo. The auditory invagina- 

 tion is cut through the centre on the left, and is more 

 advanced than it is in Fig. 2. The nerve is shown. 



Fig. 4. Similar section of an older embryo shortly before hatching, 

 i.e., about 4 mm. in length. Invagination is now com- 

 pleted, and the vesicle is pyriform. 



Fis. 5. Slightly oblique transverse section of a tadpole of 8 mm. On 

 the left the section passes through the centre of the 

 auditory vesicle, and the recessus labyrinthi is shown. 

 On the right the section passes through the anterior 

 part of the vesicle, showing the auditory ganglion and 

 the epithelium common to the two anterior ampullae 

 separating from the rest. 



Fig. 6. Diagrammatic horizontal section of a tadpole of 8 mm., to 

 show the gill clefts and arches. The fore- and mid-brain 

 are cut, as well as the nose and kidney. The five pairs 

 of clefts and six pairs of arches are represented. The 

 hyomandibular cleft does not reach the skin. 



Fig. 7. Oblique transverse section of a tadpole of 12 mm., showing 

 the beginnings of the septa which cut off the semicircular 

 canals. On the left the recessus is cut, along with the 

 outer and upper septa belonging to the anterior vertical 

 and horizontal canals respectively. On the right the 

 anterior part only of the recessus is cut, and the outer 

 ridge of the septum of the anterior vertical canal, 

 together with the lower part of the septum of the hori- 

 zontal canal : (x 25). 



Fig. 8. Section through a somewhat older tadpole than the last. On 

 the right the horizontal canal is cut, its septum being 

 completed. On the left the folds forming the septum of 

 the posterior vertical canal are shown ; they have not 

 yet met. Part of the beginning of the septum between 

 utriculus and sacculus is represented, as is the small 

 pouch representing the lagena : (x 25). 



Fig. 9. Transverse section through the centre of the ear in a tadpole 

 of 25 mm. The full extent of the recessus at this stage 

 is shown : (x 15) 



