On the Perilymphatic Spaces of the Amphibian Ear. 239 



apparently the posterior part of the latter, is however in reality the 

 anterior end of the ductus reunieus, which has undergone a secondary 

 change in position. It cannot be distinguished by observation from 

 the spatium raeningeale, with which it has become incorporated 

 (flg. 22). 



The development of the perilymphatic spaces in R. fusca appears 

 to be modified in several respects. It is especially interesting to find 

 that the first part of the system to develop is the recessus partis 

 basilaris^) (fig. 24). When the larva is about 18 mm in length, the pars 

 basilaris is situated in a well marked depression of the fioor of the 

 capsule; posteriorly to it is the recessus, which passes out through the 

 lower and outer part of the common aperture which at this stage re- 

 presents the foramen perilymphaticum inferius as well as the for. peril, 

 superius. The whole of the aperture leads at this stage into the ca- 

 vum cranii, and the fissura metotica commences at a point very slightly 

 posterior to its posterior border. The fact that the foramen perilym- 

 phaticum inferius at this stage opens apparently into the cavum cranii 

 seems to require an explanation, since in the larval Pelobates it passes 

 to the exterior of the skull. Even in the adult Rana however it is 

 not easy to define the limits of the fissura metotica. The course of 

 development in Pelobates seems to me to prove that the foramen peri- 

 lymphaticum inferius originally opened on the surface of the skull, and 

 that the condition just described in Rana — a condition only found 

 during a very short period — is secondary, as is also the origin of 

 the two apertures as a single one in this form. 



At 23 mm the recessus partis neglectae is evident, and has com- 

 menced to pass into the cavum cranii to form the spatium meningeale. 

 The ductus reuniens is at this stage neither within the cavum cranii 



^) Villy's [6] mistake in interchanging lagena and pars basilaris led him into 

 several other errors. Thus, he says "The lining of the first formed division of 

 the cochlea, i. e. the lagena, is the last to become distinct from the saccular 

 epithelium. This fact may fairly be taken to support my view that the epi- 

 thelial patches do not develop in the order in which they were evolved". Now 

 since his "lagena" is really the pars basilaris, that is to say the most recent ac- 

 quirement, the late development of its sensory epithelium requires no explanation. 

 He also errs in attributing the "Knorpelrahmen" to the lagena, as well as the 

 association with a perilymphatic space. 



