The Morphology of Cosmobia 3T!) 



modifications due to functional activity from almost the beginning of 

 development, and thus exhibits the solution of what may be considered 

 a new physiological problem, a study in Experimental Zoology made by 

 Nature herself. 



C. The Compound Middle ear of the SynoUc side. This region may 

 be taken as an especially good example of one which, in part through 

 lack of function during embryonic life, has retained its primary sym- 

 metry. The parts are at the same time sufficient in number and com- 

 plexity to express this symmetry in a high degree, and the complete 

 correspondence, even of the smallest details, is highly suggestive in the 

 present argument. 



a . ■ b 



Fig. 5. Baldwin Synote, Teras III. 



(a) Normal os tyrupanicum of the right ear of corupoiient A. 



(b) The two reduced ossa tynipanica siirrounding the synotie ossicles. 

 These consist of the right one of B and the left one of A. 



All are drawn to the same scale. 



Within the single external meatus lay the middle ear chamber, its 

 entrance framed in by a pair of tympanic bones, symmetrical in respect 

 to each other but each somewhat smaller than the normal ones of the 

 perfect side [Fig. 5]. Normally each forms a nearly complete circle, 

 the frame for the outer tympanic membrane, but on the synotie side 

 the two together framed in an oval space, its greatest diameter lying 

 transversely; of this each tympanic bone formed a little less than half 

 the circumference. Undoubtedly there was also here a tympanic mem- 

 brane, but as the parts had been subjected to maceration in caustic pot- 

 ash before examination this point cannot be determined. 



Lying within the oval tympanic frame there appeared the auditory 

 ossicles, a doubled malleus upon a doubled incus, and two distinct stapedes 



