10 GEORGE L. STREETER 



them unite in the formation of a loop at one side or at one or both 

 ends of a nucleus, thereby creating a perinuclear space which 

 soon takes on a more transparent appearance than the surround- 

 ing homogeneous material that accumulates in the place of the 

 disappearing processes. These changes can be seen in the 

 sketches shown in figure 5, which represent characteristic 

 areas in the otic capsule while in the precartilage stage in 

 human embryos 17 and 18 mm. long. In the two sketches 

 marked A the contrast beween the permanent and disappearing 

 protoplasmic processes is already noticeable. In the sketch 

 marked B the transition is more advanced although one can still 

 recognize in the homogeneous matrix remnants of branching 

 processes which have not yet disappeared. The persisting 

 processes enclose characteristic capsular or perinuclear spaces. 

 Similar spaces are shown in figure 6 which presents a series of 

 isolated nuclei with their associated permanent processes such 

 as are found in sections of maturing precartilage. In some of 

 these (figure 6, C and figure 5, B,) there is a beginning accumu- 

 lation of granular protoplasm at the margin of the nucleus which 

 constitutes the so-called endoplasm and becomes enclosed with 

 the nucleus in the capsule. After the formation of the spaces the 

 endoplasm gradually accumulates and forms the cell body of the 

 encapsulated nucleus. Thus in precartilage we find all stages 

 in the transition, from a mesenchymal syncytium to a tissue 

 consisting of partially encapsulated cell-islands separated from 

 each other by a homogenous matrix. 



CARTILAGE STAGE 



The transition from precartilage into cartilage gradually takes 

 place in the otic capsule when the embryo is between 25 

 and 30 mm. long. This maturation is characterized by an in- 

 crease in the amount of matrix combined mth a more complete 

 encapsulation of the nuclei, or cartilage-cells, as they may now be 

 designated. With the increase in the amount of the matrix 

 there is also a change in its chemical composition, so that it 

 becomes possible to stain it differentially. This tinctorial re- 

 action constitutes an arbitrary point at which it may be said 



