448 GEORGE A. BAITSELL 



The above results led naturally to the question as to whether 

 a similar process normally takes place in the histogenesis of the 

 connective tissues in amphibian embryos and thus to the present 

 study in which this problem is considered. It is worthy of note 

 that, notwithstanding the great amount of work that has been 

 done upon the development of connective tissue, no general 

 agreement has been reached. At present there are two main 

 theories held regarding connective tissue formation — the intra- 

 cellular theory and the intercellular theory — and, in general, the 

 results of the various investigators support one or the other of 

 these. In order to get the matter clearly in mind it may be 

 well to set forth a statement of the opposing views, which are 

 as follows : 



According to the intercellular theory there is early formed 

 in development an amorphous, gelatinous, non-living ground 

 substance. It is generally held that this is formed as a secretion 

 of the mesenchyme cells. Later, fibers are formed in this ground 

 substance by a deposit or secretion which is given off by the 

 cells of the tissue. It is held that the cells have no morphological 

 connection whatever with the fibers which form in the ground 

 substance. 



The intercellular theory substantially as stated above was the 

 original theorj^ held for connective tissue formation and was first 

 stated by Henle. With various minor modifications, it has been 

 supported by v. Kolhker, Alerkel, Ranvier, v. Ebner, Renaut, 

 Schafer, Laguesse, and others. The material used in the re- 

 searches of these investigators was obtained from many different 

 sources and included both embryonic and adult tissue. 



The intercellular theory has been, perhaps, most strongly 

 supported by Merkel. In his last paper ('08) he gives a splendid 

 review of the question of connective tissue development as well 

 as the results of his own studies. His conclusions are that the 

 primitive origin of all connective tissues lies in an amorphous 

 gelatinous substance which is secreted by the syncytium of the 

 mesenchyme cells. This secretion constitutes the ground sub- 

 stance and in some cases it is formed sparingly and in other cases 

 very abundantly (e.g., Amphibia, umbilical cord). The fibers. 



