416 E. T. Bell. 



this classification does not apply very well in the calf. A peculiar 

 open-meshed tissue, which I shall call preadipose tissue (Text Figs. 

 1 and 8, and Fig. 6, Plate II), precedes in every case the formation 

 of adipose tissue in the embryo. The preadipose tissue varies in 

 different regions in the quantity developed before the true fat cells 

 begin to form, and it remains in the preadipose condition longer 

 in some situations than in others ; but the differences are not marked 

 enough to warrant Hammar's classification. The term, primitive 

 fat organ, may however be retained, if desired, to designate the 

 renal preadipose tissue, since this tissue is more sharply marked off 

 than preadipose tissue in other situations and persists longer in 

 the preadipose condition. 



The primiitve fat organs. 



These were first mentioned by Kolliker in the mesentery of the cat 

 in 1856. Toldt first gave a description of them and brought them 

 to the attention of anatomists. His study of these structures, sharply 

 defined as they are in the animals he studied, led him to the belief 

 that adipose tissue is a special kind of tissue derived from these 

 organs only. He thought that all adipose tissue is derived from 

 outgrowths of these organs. He believed that the subcutaneous 

 adipose tissue is developed principally from the primitive organs 

 of the axilla and inguinal region. 



In the new-born rat Auerbach (3) describes masses of brown 

 adipose tissue (these are presumably primitive organs) in the inter- 

 scapular and interrenal region, in the axilla, neck, and thoracic 

 cavity. These organs have been described in the guinea-pig, mouse, 

 rat, cat, etc. In this paper it will not be desirable to give the detailed 

 distribution of the primitive fat organs in these animals, since, as 

 Hammar has pointed out, they have an entirely different structure 

 here to that which one finds in the calf. 



Hammar describes a primitive fat organ in the renal region in 

 man, the dog, and the calf. As far as I laiow this structure has 

 not been described by any other observer. The primitive organs 

 of the cat, etc., consist of well-defined masses of closely-packed cells 



