No. I.] THE VERTEBRATE EAR. 35 



in Petromyzon, the ear chambers would communicate only by 

 the separated ends of the endolymphatic ducts (PI. IX, Fig. 2), 

 as in the Gnathostome type, and, as will be perfectly evident 

 on the inspection of the diagram mentioned (which, although 

 a diagram, is true to the anatomical relations of the parts in 

 Petromyzon), that the lagenar sack would be divided into two 

 chambers entirely cut off from each other, the anterior or the 

 utricular being the smaller of the two and containing a portion 

 of the macula utriculi, the posterior and (two times) larger con- 

 taining the well-formed papilla lagenge and a part of the macula 

 sacculi, which laps down over the edge of the pocket. These 

 two pockets would thus communicate with the posterior inner 

 and anterior inner angles of the utriculus and sacculus respec- 

 tively. I was at first inclined to think that the cochlear and 

 utricular recesses had been formed in this manner, but the dis- 

 covery that the utriculo-saccular partition was continued cephalad 

 of the lagena, and further, that there exists in the Petromyzon 

 ear an independent utricular recess, decide the question as to 

 the value of the Cyclostome lagena. It is purely a saccular 

 pocket. 



In the higher forms the lagenar pocket appears to be given 

 off from the posterior outer angle of the sacculus, and has thus 

 been displaced backwards and outwards. 



In the bony fishes the lagena offers nothing of unusual inter- 

 est for consideration here, and it is not until we reach the 

 higher ichthyopsoid forms that the papilla basilaris, the parent 

 organ of all the genuine cochlear structures, is developed. It 

 is first produced, so far as our knowledge of living forms reaches, 

 in the Anura, among which and the lower Reptilia it remains 

 undeveloped and probably functionally insignificant. When, 

 however, we reach the Saurians, the organ undergoes great 

 changes in its structure, and in the Crocodilia reaches a condi- 

 tion of development but little if at all inferior to the Monotreme 

 cochlea. 



Alligator (PI. VII, Figs. 2, 4, 7, and 9 ; PL X, Figs. 3 and 4). 



The cochlea of the Alligator forms a depressed tube of angu- 

 lar outline and of relatively large size. It is curved in two di- 

 rections, but not in as marked a degree as in Mammals and some 

 Birds, though it approaches the Monotreme condition in this 



