Histogenesis of the iVdipose Tissue, 417 



rich in protoplasm; but in the calf, man, and dog these structures 

 are composed of a reticular tissue with branched cells. 



Preadipose tissue of the calf. 



I have not used the term "primitive organ" in my descriptions 

 in the calf since, as will appear later, it seems to make a distinction 

 of no fundamental importance. 



Renal preadipose tissue. Hammar finds this tissue first in a 11.5 

 cm. foetus. He found no trace of it in a 5 cm. foetus. He describes 

 it as appearing first as a sheet of tissue parallel to the surface of 

 the kidney. Later it branches to form lobules. The fat cells begin 

 to appear in masses around the blood vessels (30.5 cm.-41 cm.). 



My own observations agree essentially with those of Hammar. A 

 4.7 cm. foetus showed a very early stage of the renal preadipose 

 close to the kidney on its ventral surface. The preadipose tissue 

 has at all times a characteristic reticular appearance in sections 

 which enables one to distinguish it readily from the adjacent tissue 

 in which the general direction of the fibers is parallel to the surface 

 of the kidney (Text Figs. 2 and 3). In the 4.7 cm. specimen it 

 forms a very thin layer (3 or 4 meshes deep), extends only a short 

 distance on the kidney, and passes gradually into the adjacent 

 tissue. 



In a 9 cm. foetus there is a continuous sheet of the preadipose 

 tissue along the ventral surface of the kidney. Its greatest thickness 

 is about 225 microns. 



In a 12 cm, foetus the greatest thickness of the sheet of preadipose 

 tissue is about 375 microns. It tapers out on the edges. 



Text Fig. 2 shows a transverse section of the body vertical to 

 the surface of the kidney (^•) of an 18,5 cm, foetus. The preadipose 

 tissue {R P) is in the form of a sheet, 450 microns thick at its 

 thickest portion, and parallel to the surface of the kidney. It is yet 

 unbranched. ISTo true (rounded) fat cells are present. Blood vessels 

 {h v) oi considerable size are to be seen. It is fairly well marked 

 off from the adjacent tissue except at the extremities where it seems 

 to be growing rapidly. 



