302 GEORCxE L. STREETER 



cartilage. The membrana propria that supports the epitheUal 

 })art of the hi})yrinth and the perichondrium lining the cartilage 

 are both derived from this periotic reticulmn. It is also a 

 modification of the meshes of this same reticulum that results 

 in the formation of the perioticular spaces in a manner that will 

 now be outlined. 



Unmodified periotic reticulum is characterized by a rather 

 uniform narrow mesh. The essential change which it under- 

 goes in the process of space formation consists in the disappear- 

 ance of some of the trabeculae of the mesh followed by the coales- 

 cence of the corresponding adjacent spaces. The trabeculae 

 consist of the protoplasmic processes of the constituent cells 

 of the reticulum and their disappearance is probably to be 

 explained, not by a dissolution or liquefaction of these cell- 

 processes but by an alteration in their form. It apparently is 

 the result of an active motility of the cell protoplasm involving 

 the successive detachment and retraction of the trabeculae. 

 When a trabecula becomes detached it gradually retracts and 

 adapts itself to the formation of a larger space, reshaping itself 

 either as a smooth border or as a constituent part of another 

 trabecula. As spaces become larger they require longer tra- 

 beculae, and as trabeculae become longer they also tend to 

 become thicker. 



The differentiation of the margin of the periotic spaces con- 

 stitutes the final feature in their maturation. During the period 

 in which the enlargement of an individual space is actively 

 going on, the margins of the main cavity consist of smooth 

 delicate strands of nucleated protoplasm that resemble the 

 trabeculae between the large reticular spaces. These linear 

 margins are interrupted here and there by openings into adjacent 

 spaces. They tend, however, to form a continuous line that 

 definitely marks off the space from the adjacent reticulum. 

 As the space becomes more mature, the membrane-like border 

 becomes thicker until it reaches a state that will probably not 

 admit of any further opening-up for the coalescence of additional 

 spaces. Any further growth is thereafter limited to simple 

 distention of the wall of the space with the consequent adjust- 



