172 FRANCIS VILLY. 



arrangement obtains ; for in frog tadpoles of only 25 mm. in length, 

 these canals have attained to the permanent condition in all essential 

 points. The toad only differs from the frog in the fact that the first 

 canal never leaves the protection of the auditory capsule in its course 

 to the skull. It runs through a special foramen immediately behind 

 the second canal, and in a. position similar to, but somewhat lower 

 than, its point of exit, and so directly into the skull. Within the 

 skull both join as in the frog, and from this common part a large 

 diverticulum runs down through the glossopharyngeal foramen, and 

 occupies a position similar to the corresponding part in the frog. 

 Thus the frog and the toad agree, except in the relative positions of 

 the foramina through which the first canal and the glossopharyngeal 

 nerve pass. 



Dactylethra I have cut as a small larva, the legs being present, but 

 as yet neither large nor pentadactylous. In this specimen the peri- 

 lymphatic spaces are present and connected with the cochlea as in 

 the frog; but they differ from both frog and toad in that they 

 communicate with each other within the capsule, and then pass out 

 by a common duct into the skull. Just where this duct enters the 

 skull a dilatation is present, passing through the foramen of the 

 glossopharyngeal nerve, and lying close above the pharynx as in the 

 frog and toad. I may mention that my Dactylethra specimen seems 

 to show a continuity of these canals of the two sides across the floor 

 of the brain case. I feel sure that this is not so in the other animals 

 examined, and this, together with the imperfect condition of my 

 Dactylethra, makes it very doubtful whether any such connection 

 really exists. 



The most interesting point in the development of this system is 

 that in both cases the canals first appear in close connection with the 

 parts of the cochlea with which they are ultimately to be associated. 

 At about 1 6 mm. the lagena becomes flattened as in the adult, and 

 the beginning of its canal is to be seen as a small sac in the peri- 

 lymph applied to the lagena as already mentioned. It is formed by 

 mutual separation of the mesoblast cells in the vicinity of the 

 lagena, and the cells so separating constitute the walls of the canal. 

 The second canal appears soon after in a precisely similar manner, 

 and the two grow towards the brain, meet, and unite. The growth 

 of the auditory capsule and skull occurring at this time, separates 



