No. I.] THE VERTEBRATE EAR. 225 



As regards the macula abortiva (macula neglecta, Retzius) in 

 the Mammalia, there are two views ; though there can be little 

 doubt that Retzius is essentially correct in his conclusion that 

 this sense organ has disappeared from the mammalian ear. 

 Hasse objects to this view, on the ground that such important 

 structures as sense organs, when once the)/- have been fully- 

 formed, are not likely to disappear again ; and since Henle and 

 Reichert had described a small branch of the saccular nerve 

 which they traced to what was supposed by them to be a small 

 macula located in the sacculus near the dividing line between 

 it and the utriculus, he concluded that the crista abortiva was 

 really present in the mammalian ear. Retzius has more recently 

 instituted a systematic search for this nerve branch and end 

 organ in preparations of the human ear as well as in dissections 

 of other mammalian ears made especially for this purpose, and 

 has failed to find the slightest trace of such structures. He 

 consequently concludes that the earlier observers were in error, 

 and that tJiis sense organ has disappeared from the mammalian 

 ear. 



Although I have shown that the crista abortiva is never a fully 

 developed sense organ, being an abortive organ from its first 

 appearance in the vertebrate series among the fishes until the 

 waning powers of the parent organ fail to give birth to the 

 organ at all (as in the mammalian group), it is not impossible 

 that this sense organ may still occur in members of the lower 

 mammalian groups, — e.g. the Monotremata, — or even that it 

 may occasionally appear as an atavism in individuals of the 

 . higher orders. At the present time, however, we do not know 

 of such instances, unless the observations of Henle and Reichert 

 are correct. Admitting that such atavism may occur, Retzius's 

 conclusion still remains essentially true. In either case the 

 plan of the distribution of the nerves remains the same. It is 

 evident from the history of this part of the ear that there is 

 from the first a tendency toward the reduction of the parts first 

 to appear in favor of the cochlear region, which steadily in- 

 creases in functional importance and receives an ever-growing 

 nerve supply. This nerve branchlet is not the only one which 

 has disappeared during the transformation of the piscine into 

 the mammalian ear ; for we know of another branchlet occurring 

 in forms as high as the reptiles which has ceased to be devel- 



