AREOLAR TISSUE. 117 



cell. Last of all, the nucleus also disappears, and fibrils alone 

 remain. All these transformations proceed in a homogeneous 

 cytoblastemaj which probably also continues to exist between 

 the fibres of areolar tissue in the adult. 



b. Adipose cells. In the later periods of foetal existence, 

 adipose cells occur in many situations in addition to the fibre- 

 cells before described. They are usually first seen in small 

 groups between the fibre-cells. They are round cells of very 

 various sizes, which are generally completely filled by a single 

 fat-globule. The cell-membrane which closely encompasses 

 the contents, is most minutely granulous, or, according to 

 Gurlt, homogeneous. It is in most instances very thin, being 

 about half the thickness of a blood-corpuscle, but sometimes it 

 is much thicker, and in the subcutaneous areolar tissue of the 

 thigh of a rickety child, at the age of twelve months (probably 

 in connexion with the disease), was almost as thick as the 

 breadth of a human blood-corpuscle. In the early stage, this 

 cell-membrane encloses a very distinct nucleus of a round or 

 oval form, which is sometimes flattened. When the former is 

 thin, the nucleus presents itself externally as a little promi- 

 nence upon the round fat -globule, which is closely encom- 

 passed by the cell-membrane ; but when thick, the nucleus lies 

 embedded in it. It contains one or two nucleoli. It is not 

 uncommon for adipose cells to contain a number of small 

 globules instead of one fat-globule, in such instances, one of 

 them is generally remarkable for its larger size. The adipose 

 cells are best seen in the fat found in the cranial cavity of a 



m 



young carp, before it has attained the length of six inches. 

 (See pi. III. fig. 10.) They there lie in so soft a substance, 

 that they may be insulated without any difficulty, and float 

 singly in the water in which they are examined. Some are so 

 larsre as to be visible even with the unaided eve. When 

 examined under the microscope with a magnifying power 

 of 450, the cell-membrane is readily recognized, it is very 

 thin, and closely encompasses the contents. It rises into 

 a little prominence on one side, within lies a proportion- 

 ately large, and very beautiful cell-nucleus, which is oval, 

 but not flattened, and contains one or two very distinct 

 nucleoli. Some of these fat-cells have two such nuclei, which 



