588 SCIENCE PROGRESS 



crocodile, with its long basilar membrane stretched in a corre- 

 spondingly elongated cartilaginous frame. 



In all the reptiles, with the possible exception of the crocodiles, 

 the changes in the structure of the cochlea are apparently 

 quantitative rather than qualitative. The sense cells still have 

 the diffuse arrangement of those of an otolith organ. They 

 show no regularity in disposition or variations in size, nor 

 are they supported in any peculiar manner. In fact the sense 

 organ has as yet assumed none of the special features of the 

 organ of Corti. 



It is curious how bird-like the cochlea of the crocodile is. It 

 stands quite apart from that of other reptiles and shows many 

 peculiarities of structure, insignificant in themselves but of the 

 greatest interest as the shadowy rudiments of important struc- 

 tures still to come. Thus, the basilar membrane is not only long 

 but differs in width in different parts and contains a layer of 

 stretched diagonal fibres ; the elements in the sense organ show 

 a distinct tendency towards orderly linear arrangement and a 

 structural differentiation amongst themselves ; the membrane 

 floating above the sense organ {tectorial membrane) is now for 

 the first time anchored along one edge to the supporting frame 

 of the basilar membrane, stretching out hood-like over the 

 surface of the sense organ. 



All these slight changes are worthy of the closest attention 

 for they are in embryo characters peculiar to the cochlea in its 

 more perfect developments and indicate the rise among the 

 higher reptiles of an auditory organ not simply sensitive to 

 sound but probably to some extent capable of resolving com- 

 plex tones into their components and thus of judging the 

 musical quality of sound. Here in fact for the first time, in the 

 crocodiles and birds, we meet with an auditory organ of some- 

 thing the same kind as our own. 



Although the cochlea in mammals is always unmistakably 

 mammalian, in the monotremes it has not yet shaken off all 

 traces of the reptile. While these traces are just in process 

 of elimination we may digress for a moment to reconsider and 

 complete their history. 



The first is a small sense organ to which we have not 

 hitherto alluded. It is known as the macula neglecta (fig. 2, Mac. 

 ngl.) and was discovered by Retzius in many fishes. Although 

 present in most fishes, it reaches the height of its importance in 



