CONNECTIVE TISSUE IN AMPHIBIA 457 



In the discussion of the earher stages, it has already been noted 

 that not only is the ground substance formed prior to the advent 

 of the mesenchyme cells but also, in some regions, it shows from 

 the earliest stages a fine fibrillation. In the stage shown in figure 

 4, this fibrillation of the ground substance has markedly increased 

 and it is found that practically all the ground substance is 

 permeated with the fibers. In some regions the fine fibers have 

 united to form fibrous bundles and in general there appears to 

 be a tendency for this to take place. A careful study of this and 

 similar preparations reveals the fact, as is depicted in the figure, 

 that there is no morphological connection between the cells 

 which are present in the ground substance and the fibers. The 

 latter have formed directly from the ground substance by a 

 modification of the elements of which it is composed. 



The preparations give evidence that the movements of the 

 cells through the ground substance may supply, in part at least, 

 a mechanical factor which aids in the formation of the fibers. 

 For example, it will be noted in figure 4 that the fiber formation 

 is particularly heavy in the portion of the ground substance lying 

 near the ventral opening in the muscle tissue through which, 

 apparently, a number of the amoeboid cells have wandered into 

 the ground substance. The preparations show many similar 

 instances of regions in which the movements of the cells through 

 the ground substance have supplied a mechanical stimulus and 

 thereby brought about the fiber formation. There is also the 

 possibility that the cells in their movements may have some 

 secretory action which also modifies the ground substance. 

 However, this point is clear from the study of the preparations 

 and should be emphasized that in no case has any morphological 

 connection been found between the cells in the ground substance 

 and the fibers. 



In this connection attention should be called to the results 

 previously obtained by the author ('17) in certain of the studies 

 on the plasma clot in which it was demonstrated that, under the 

 influence of certain mechanical factors, it was possible to trans- 

 form a homogeneous fibrin clot into a fibrous tissue which, in 

 its morphology, very closely resembled various types of fibrous 



