CONNECTIVE TISSUE IN AMPHIBIA 463 



In connection with this point, MerkeP*^ rightly calls attention 

 to the fact that it is only the formation of the fibers in the first 

 stages of connective tissue development concerning which there 

 is a difference of opinion at present. For a long time there has 

 been no question but that in the later stages of connective tissue 

 development there is a complete separation of fibers and cells. 

 Since this is the case, the logical conclusion appears to be that 

 the fibrillar structures which are present in the connective tissue 

 cells at certain times are not connective tissue fibers, for there 

 is no apparent reason why the fibers in the early stages of con- 

 nective tissue development should be formed in the cells and 

 later the process change and the fibers be formed in the ground 

 substance independently of cells. 



Considerable stress has been laid at times upon the spindle 

 shape of the connective tissue cells or fibroblasts. I regard the 

 shape of the connective tissue cells as almost entirely dependent 

 upon the external factors which the cells encounter. The study 

 of the material shows that when the mesenchyme cells first 

 enter the ground substance they are, in general, rounded, typi- 

 cally-shaped cells. Later, in the ground substance, they assume 

 various irregular shapes, as shown in figure 4, among which will 

 be found a number of spindle-shaped fibroblasts. The idea has 

 been more or less prevalent that cells of the spindle type are in 

 some way 'spinning fibers' and therefore the shape has been 

 regarded as a constant factor for the fibroblasts. The studies 

 of various types of cells in tissue cultures^'' show that the shape 

 of the cell is not a constant factor. Certain cells w^hen grouped 

 together in the cell masses show a typical cell body. The same 

 cells when separated assume various irregular shapes, such as 

 stellate, amoeboid and spindle, depending upon the nature of 

 the medium and whether the cell is exhibiting movement. If 

 the cell begins to move in a certain direction along a fiber or 

 other support it will elongate in a direction parallel to the move- 

 ment and assume thereby a spindle shape. ^^ It is believed, 



i^Merkel, 19C8, p. 381. 



« Harrison, 1914, pp. 535-8. Cf. Figs. 8-12. Matsumoto, 1918, pp. 555 et seq. 



17 Harrison, 1914. Cf. figs. 4-7. 



