CONNECTIVE TISSUE IN AMPHIBIA 459 



ventrally in the median line. From the median region of the 

 embryo the connective tissue sheet extends laterally in either 

 direction among the bands of muscle fibers — transverse sections 

 of which are to be seen in the figure — until the body wall is 

 reached. Between the body wall and the muscle tissue there is 

 also a compact layer of the connective tissue. The fibrillation 

 of the connective tissue is heaviest around the notochord. In 

 the region of the muscle tissue the fibrillation is comparatively 

 light and the ground substance closely resembles in its structure 

 that found in 3'oung tadpoles as shown in previous figures. 

 Under a higher magnification it will be seen that numerous 

 sp:nd:e-shaped cells are scattered in various regions of the prep- 

 aration lying in cavities on the connective tissue. In some cases 

 they are stretched along the bundles of fibers. Here again the 

 Mallory stain shows a clear differentiation between the cytoplasm 

 of the cell bodies and the common ground substance in which 

 they are imbedded and in no case has it been possible to demon- 

 strate any morphological connection between the cells and the 

 fibers. 



DISCUSSION 



The researches of Studnicka ('03), Hansen ('05), Mall ('02) and 

 others, upon various phases of connective tissue development in 

 different species of animals, demonstrate conclusively that a 

 rigid adherence to the intracellular theory, in which it is held 

 that the fibers develop directlj^ through a transformation of cell 

 cytoplasm, is no longer possible. The result has been that the 

 intracellular theory as originally stated has been modified by 

 the Hansen-Mall theory which holds, as stated earlier in this 

 paper, that the fibers develop, in general, in a common, living 

 intercellular material, termed the exoplasm, which has been 

 formed as a result of a syncytium of the mesenchyme cells. 



At the present time, the inadequacy of the unmodified intra- 

 cellular theory has been recognized even by Flemming, whose 

 work on the development of connective tissue fibers in the 

 Salamander larvae ('91) is generally regarded as the corner stone 

 of the intracellular theory. Flemming admits that the results 



