170 FRANCIS VILLY. 



wards. The distal enlarged part grows, and, as the tadpole loses its 

 tail, assumes the permanent proportions, becoming at the same time 

 thin-walled and vascular, and the organs from the two sides meet 

 both above and below the brain. Whether actual communication is 

 set up is difficult to determine by means of sections alone. 



The growth of cartilage between the expanded end of the organ 

 and the rest of the vestibule does not take place till late, and even 

 then a foramen is left, through which the duct passes from the 

 vestibule into the skull cavity. 



The development of this structure shows that the whole of it is 

 part of the internal ear, and is not to be associated morphologically 

 with the lymphatic spaces within the skull. No opening from the 

 expanded portion within the skull is to be found connecting it with 

 other cavities in any way. 



/. The Perilymphatic Spaces. — This system of canals has never been 

 described adequately, although it is distinctly developed and very 

 obvious in sections passing through the hinder part of the ear. 

 Hasse and Retzius* have both given accounts of parts of these 

 canals ; but I believe that they have considered the two to be abso- 

 lutely continuous with each other, and have described as one what 

 really consists of two distinct parts. The canal which I have taken 

 as the first is carefully described ; but the second seems to be taken 

 as forming the anterior part of the first. Its passage into the skull 

 through the foramen rotundum is not described, and the close 

 relation of both to the parts of the cochlea is not noticed. I have 

 investigated the course of these canals in the common frog, the toad, 

 and Dactylethra larva. 



In Puma temporaria the system is composed of two canals in the 

 hinder part of the ear, closety connected with the cochlea, and 

 communicating with each other within the skull. The walls consist 

 of a single layer of much flattened cells, and backing this layer 

 there are a few scattered cells lying in the perilymph. These walls 

 are distinct though thin at all points in the course of the canals, 

 which therefore do not communicate with any other system. 



The first canal to be described, the ductus perilymphaticus, is in 

 close relation with the lagena. The walls of the extremity of this 

 part of the cochlea are very different on the inner and outer sur- 



* " D. Gehororgaii d. Wirbelthiere," 



