Observations on the Labyrinth of Certain Animals. 285 



the same or°;an in the other ungulates was found to be slight. There were no 

 exceptions to the rule in the rodents : the rat, the mouse, the guinea-pig 

 and the rabbit all being possessed of sharp-pointed cochleae. Three monkeys 

 were examined and no exception was found, the cochlea being in every 

 case of the flattened type and very like that of man, bixt smaller. The 

 organ in the lemur was also of the flattened type, as was that of the 

 porpoise. 



The perilymphatic space of the semicircular canals proved to be a very 

 interesting study. Our ideas of the anatomy of the labyrinth have depended 

 so much upon the investigation of the organ in the human subject that it is 

 not surprising that errors have crept in by assuming that certain features 

 found in Mm will also be found in the lower animals. The present is a case 

 in point. The perilymphatic space in the canals of the human subject is 

 large and well developed, and it has been assumed that this would be true of 

 other animals. But such is not the case. It so happens that man is one of 

 the exceptions to a general rule. In mammals the ride is that the peri- 

 lymphatic space is either very small or even completely absent in the canals. 

 The exceptions to this rule are: — man, the monkeys, and the seal. No doubt 

 there are other exceptions ; indeed, another falls to be recorded in this paper, 

 but a sufficient number of examples have been examined to assert that the 

 rule above given is a fairly general one. 



In spite of the existence of this general rule, however, it is probable that 

 the original type of the mammalian labyrinth possessed a well-developed 

 perilymphatic space in the canals. The chief reason for this belief is, that 

 in the reptiles and birds this is the type invariably found in all the animals 

 of those divisions which have been examined. A more definite statement 

 will be possible when the labj^rinth of the monotremes has been investigated 

 in regard to this feature. One of these is at present in course of preparation, 

 and the results of the examination will be published later. At present we may 

 regard the presence of a well-developed perilymphatic space in the canals 

 as indicating a labyrinth of a more ancient type. This, of course, does not 

 mean that the particular species which possesses such a labyrinth is there- 

 fore an ancient species. Obviously, man is a very recent species of animal, 

 although he possesses the space referred to above. It merely means that 

 man's progenitors have not dispensed with the space when other species of 

 mammals were in process of losing it. 



The presence or absence of this space is therefore a valuable guide to the 

 relationship of different orders and species of mammals. Its value is 

 enhanced by the fact that the space does not appear to have any physiological 

 function. It is found in animals which have great delicacy of movement, and 



