THE HISTOGENESIS AND GROWTH OF THE OTIC CAPSULE AND ITS 



Furthermore, it can not be the perichondrium that is the essential factor, either in 

 the deposit of new cartilage or in the excavation of the old, because the perichon- 

 drium, as we shall see, is not formed until after a considerable amount of the growth 

 and hollowing-out of the labyrinth is already completed. Therefore, in the devel- 

 opment of the cartilaginous capsule there is something more than interstitial and 

 perichondrial growth. 



As forming at least one element, and an important one, in this process it has 

 been found that there occurs a regression of certain areas of cartilaginous tissue to a 

 more embryonic form followed by its alteration into a different type of tissue. It is 

 this process of dedifferentiation that constitutes the essential factor in the hollowing- 

 out and reshaping of the otic capsule which take place continuously during its 

 development. Though the significance and wide occurrence of dedifferentiation 

 and redifferentiation have been well known to botanists and to those investigators 

 who have worked with the simpler forms of animal life, this, as far as the writer 

 knows, is the first time that they have been shown to occur in the human embryo. 

 It is not unlikely that these principles will eventually enter into our conception of 

 the growth of other tissues and organs in human as well as in other mammalian 

 embryos. The establishment of this point, of the occurrence of retrogressive as 

 well as progressive differentiation in human embryos, is considered by the writer to 

 be the chief contribution of the following paper. 



The fate of the periotic connective tissue that intervenes between the cartilage 

 and the membranous labyrinth and the formation of the characteristic periotic 

 spaces form problems that are naturally of a morphological character. These spaces 

 have been studied by modeling methods and a description will be given of the steps 

 by which the larger spaces acquire their adult form. It will be pointed out that 

 these spaces show a marked individuality. They have constant and definite charac- 

 teristics, including their time and point of origin, the manner in which they spread, 

 and their eventual form and structure. They have a structural individuality which, 

 though less complicated, is just as definite as that of the other parts of this sense- 

 mechanism. All of this we will come to later. 



TERMINOLOGY. 



The writer is not unmindful of a certain feeling of distress that is aroused when 

 it is found on reading a new paper that the author of it is adding to the already 

 difficult matter of following another's description by making a new application of 

 terms or by introducing a whole battery of freshly created ones. Nomenclature 

 constitutes one field in which rock-bound conservatism has many points of merit 

 and where originality may expect a cold and critical reception. It is therefore 

 with some embarrassment that the writer approaches the subject of terminology, 

 and it is also with some apprehension as to whether the "originality " in this instance 

 will prove to be justified. It has in fact seemed best to avoid the incorporation 

 of the term "lymphatic" in describing of the tissue-spaces surrounding the mem- 

 branous labyrinth. It has been the custom to designate these as " perilymphatic " 

 spaces since 1 x;i:>. when the term was introduced by Breschet, who thus distinguished 



