64 



CONNECTIVE TISSUE CAETILAGE BONE 



FIG. 76. ADIPOSE TISSUE. 



The fat cells have been blackened by osmium 

 tetroxid. X HO. 



8, 2, 1914) fat cells 

 can arise also by a 

 process involving the 

 enclosure of free fat 

 spherules by endothe- 

 lial cells. They suggest 

 that fat cells may be 

 modified endothelial 

 cells rather than mod- 

 ified fibroblasts. 



The forerunners of 

 the original smallest 

 fat droplets are gran- 

 ules (Altmann, 1890). 

 In the subcutaneous 

 tissue of Myxine (Hag- 

 fish) embryos, Schrei- 

 ner (Anat. Anz. 48, 7, 1915) has described the process of fat elaboration 

 in minute detail. The pre-fat granules originate from rod-like chromidia 

 ('mitochondria') by process 

 of segmentation. The chro- 

 midia arise as nucleolar buds 

 which wander through the 

 nucleus and traverse the nu- 

 clear membrane as spherical 

 granules. These 'primary 

 granules' elongate into rods, 

 and subsequently segment into 

 'secondary granules/ which 

 liquefy and coalesce to form 

 the definitive fat spherules. 

 This important investigation 

 suggests a functional role for 

 mitochondria in terms of a 

 nutritive material upon which 

 cell metabolism and differen- 

 tiation may depend. 



Lymphoid Tissue (Ade- 

 noid Tissue). Lymphoid tissue is a reticular tissue the meshes of whose 

 network are occupied by a closely packed mass of lymphocytes, cells with 



FIG. 77. DEVELOPING ADIPOSE TISSUE FROM 

 THE SUBCUTANEOUS TISSUE OF AN INFANT. 



The fat has been removed by immersion in 

 alcohol and ether. The polygonal outlines of 

 the fat cells are well shown. Within many of 

 them is seen the finer cytoplasmic network by 

 which the inclosed droplets of fat were in- 

 vested; this network had not been completely 

 replaced by the accumulation of fat. Hema- 

 tein and eosin. Photo. X 325. 



