464 GEORGE A. BAITSELL 



therefore, that the spindle shape of a cell indicates a response 

 to the environment and not a process of fiber formation. 



With regard to fiber formation the present work demonstrates 

 that the fibers may develop in regions of the ground substance 

 which are free from cells. At later stages when cells are present 

 the study of the material gives no evidence of any morphological 

 connection between them and the fibers in the ground substance. 

 The complete [^process of fiber formation from the ground sub- 

 stance can be observed and the transformation into a fibrous 

 tissue appears as a gradual development from a fine fibrillation 

 through various stages until the well developed fibrous condition 

 is reached. 



The previous studies of the author, with the plasma clot, show 

 clearly how a morphological transformation of this character 

 may take place, by means of a fusion and consolidation of the 

 minute elements of which the clot is composed, in response to 

 mechanical factors such as tension or pressure. It was sug- 

 gested at that time^^ that "a reaction of this kind plays an impor- 

 tant part in the ontogeny of the individual in the formation of 

 the various connective and supporting structures. The well 

 known fact that they, in general, are laid down in exact corre- 

 spondence to the definite stresses of the organism leads to the 

 conclusion that in their formation some arrangement must have 

 been present which would respond to the various mechanical 

 factors introduced during development, such as has been shown 

 to be the case with the plasma clot. The generally accepted view 

 of the intracellular origin of the connective tissues does not give 

 any adequate explanation of this fact." 



From the morphological standpoint, the results of the present 

 study indicate that the formation of connective tissue in the 

 amphibian embryo is similar to the process which takes place in 

 transformation of the plasma clot. The intercellular ground 

 substance of developing connective tissue may therefore be 

 compared in its morphology to the plasma clot. This ground 

 substance when first formed appears homogeneous or with a 



'8 Baitsell, 1917, p. 130. 



