170 TEXT-BOOK OF EMBRYOLOGY. 



feature, and while it may increase independently of the cells it must primarily 

 have a cellular origin. 



Fibrillar Forms. The first type of connective tissue to be derived from 

 the embryonic non-fibrillar form is areolar tissue. Areolar tissue is composed 

 of comparatively few cells and much intercellular substance, the latter in turn 



- FIG. 145. Fibril-forming cells from fresh subcutaneous tissue of head of chick embryo. Boll. 



being composed of fibers and "ground substance." The fibers are of two 

 kinds, "white" or fibrillated and "yellow" or elastic. To this type of tissue 

 in the embryo the term embryonic connective tissue has been applied. 



The origin of the fibers is an unsettled question. Some investigators hold 

 that they are derived from the homogeneous "ground substance" by a process 



FIG. 146. Connective tissue (mesenchymal) cells from larval salamander. F lemming. 



of differentiation (Ranvier, Merkel). The view that is best supported by 

 direct observation, however, is that the fibers are derived from the cells 

 (Boll, Spuler, Flemming). The cytoplasm at the periphery of the cells and 

 their processes becomes differentiated into extremely delicate fibrillse which 

 become grouped into bundles (fibers) and then become separated from the 



