26 AVERS. [Vol. VI. 



Periost des knochernen Aquaductus vestibuli und an seinem 

 hinteren blinden Ende von der Dura mater dicht umschlossen." 

 A condition of things which I have often observed, and which, 

 when we recall the embryonic condition in connection with the 

 permanent arrangement in sharks, receives its explanation. 



The semi-gelatinous mass of the embryo, which occupies the 

 foramen for the ductus endolymphaticus is ultimately obliterated, 

 being encroached upon by the ossifying membrane bones and 

 closely invested, since the whole of these structures lie within 

 the dermal zone. The perilymphatic spaces are confined to 

 those parts of the canal complex which retain the primitive 

 chondrocranial capsule, to which the ossific processes are con- 

 fined. 



The sense organs of the internal ear have not been studied 

 from the standpoint of their descent from superficial canal 

 organs, and I think this in many ways fortunate for my demon- 

 stration. For we find in the literature numerous accounts of 

 the development of the auditory nerve-end organs in several 

 vertebrate forms, which agree in a remarkable manner with 

 the accounts given of the development of the canal organs. 

 We are thus provided with a valuable fund of knowledge that 

 is certainly entirely unprejudiced and thoroughly independent. 

 This evidence I shall give further on. Just here I shall give an 

 account merely of the shape of these sense organs and of their 

 position within the ear cavity. The so-called maculcE all lie 

 within the larger cavities of the ear, but are not separated from 

 the crist(E by any sharply defined characters such as would seem 

 to be indicated by the older accounts of them and by the termin- 

 ology applied to them. 



They are usually oval bodies, and are seldom irregular in shape. 

 They may be circular, or drawn out into bands. They lie flat 

 upon the walls of the ear chambers in which they are placed, 

 and do not show the tendency to elevation observed in the 

 cristae or ampullar sense organs. The hair cells are thus placed 

 on a level floor, and none of the hairs project beyond their 

 neighbors, unless by reason of superior length. The utricular 

 end organ — macula aciistica iitricidi — of many Elasmobranch 

 species, and from here on throughout the remaining members 

 of the vertebrate group, frequently appears in part as a seri- 

 ally arranged patch or row of sense organs, — indeed, such is 



