44 THE HISTOGENESIS AND GROWTH OF THE OTIC CAPSULE AND ITS 



in figures 30 and 31, which present median and lateral views of a wax-plate model 

 of a human fetus 130 mm. crown-rump length (Carnegie Collection, No. 1018). 

 On comparing the scala tympani and scala vestibuli as seen in these figures with 

 those in figures 28 and 29, it will be seen that they are larger in cross-section and 

 more nearly cover the cochlear duct. Furthermore, they now extend to the extreme 

 tip of the duct and communicate with each other across its central margin, thus 

 forming a helicotrema. A section through this point can be seen in figure 25, in 

 which these structures are shown as seen under low magnification. It will be 

 noted that now, even as far as the tip of the cochlea, each of the scalse consists of 

 a continuous principal space, though both are more mature and larger in their 

 proximal portions. Along the first turn of the cochlear duct they are walled off 

 by a smooth membranous margin which separates them from the adjacent reticular 

 tissue. The spaces of the latter do not seem to be taking any further part in the 

 process of enlargement of the scalse. Along the second turn of the cochlear duct, 

 a section of which is shown in figure 20, the coalescence of reticular spaces with 

 each other and with the scalse is still in active operation. This produces a greater 

 irregularity of the scalse than is shown in the model. The subsidiary spaces are 

 shown as a solid mass; the slender clefts separating them are not represented. The 

 nearer one approaches the tip of the duct the more immature are the scalse, until 

 the condition is reached that is shown in figure 25, where the membrane-like margin 

 is quite incomplete and the spaces merge irregularly with the surrounding reticulum. 

 Thus a single specimen, if studied in its different parts, shows several stages in this 

 interesting process of the formation and growth of the scalse. 



The figures grouped on plate 3 illustrate some of the histological features 

 of this process. An early stage in space-formation is shown in figure 23. This 

 is a section through the canal region where the changes in the reticulum are late 

 in making their appearance. In fact, the periotic spaces never reach the same 

 degree of differentiation here that occurs in the case of the cistern and scalse. The 

 initial steps, however, are the same, and this figure presents very well the appear- 

 ance of the periotic reticulum as it begins to open up into larger spaces. Unmodi- 

 fied reticulum is characterized by a rather uniform narrow mesh. The essential 

 change in space-formation consists in the disappearance of some of the trabeculae 

 of the mesh, with the consequent coalescence of the corresponding adjacent spaces. 

 The trabeculse consist of the protoplasmic processes of the constituent cells of the 

 reticulum and their disappearance is to be explained in either of two ways: It is 

 possible that owing to some property of the fluid element of the tissue the proto- 

 plasmic strands are dissolved or liquefied; this would account for their complete 

 disappearance. On the other hand, the same result could be accomplished by an 

 alteration in the form of the cell processes. A given trabecula could separate at 

 either end, or at some point along its line, and the free ends of protoplasm could 

 then retract and reshape themselves and become a part of the remaining frame- 

 work. Whether we are dealing with a liquefaction of tissue or with active motility 

 of the cell, protoplasm involving detachment and retraction of the trabeculse can 



