456 GEORGE A. BAITSELL 



The presence of a ground substance formed prior to the appear- 

 ance of the mesenchyme cells has been demonstrated by various 

 investigators but notably by Szily ('07) who, working on chick 

 and fish material, says^ ''Vor dem Auftreten der Mesenchym- 

 zellen sind die Liicken and Spalten der Embryonalanlage durch 

 ein feines Fasersystem ausgefiillt." He holds, however, that 

 this cell-free, fibrous, supporting tissue, instead of being a secre- 

 tion from the cells, arises from fine fibrous protoplasmic processes 

 of the epithehal and endothelial cells. The mesenchyme cells 

 appear later and enter into a protoplasmic union with the fibers 

 already present. The embryonic connective tissue is made up 

 of the mesenchyme cells and the fibrillar intercellular material. 

 The mesenchyme cells furthermore serve for the nourishment 

 and growth of the fibers which, in the meantime, have become 

 separated from the cells of which they previously formed a part. 

 Szily therefore believes that, in the formation of the embryonic 

 supporting tissues, all three of the primary germ layers take an 

 active part, and the final product is a mixed tissue in which the 

 product of any one germ layer cannot be identified. 



The present work agrees with the work of Szily in demonstrat- 

 ing the presence of a primitive ground substance prior to the 

 advent of the mesenchyme cells. No evidence has been found, 

 however, of its formation by means of protoplasmic processes 

 of the surrounding cells. The study of the embryonic cells in 

 the amphibian material, at the early stage at which the primitive 

 ground substance is formed, shows them to have a clear, sharply 

 defined, regular membrane with no processes of any kind. There 

 is no question but that with a differential stain, such as Mallory's 

 which was used, protoplasmic processes could be demonstrated 

 if the}^ were present. It is easy enough to do so a little later 

 with the mesenchjane cells when they wander into the primitive 

 ground substance as shown in figures 4 and 6. The conclusion 

 is, therefore, that the primitive ground substance in the amphi- 

 bian embryo arises as a cellular secretion and not by the fusion 

 of cytoplasmic processes. 



8 Szily, 1907, p. 741. Cf. also Isaacs, 1919. 



