cell. Last of all, the nucleus also disappears, and fibrils alone remain. All these transformations proceed in a homogeneous cytoblastema, 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 prominence upon the round fat-globule, which is closely encompassed 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 young carp, before it has attained the length of six inches. (See pl. 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 large as to be visible even with the unaided eye. 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 proportionately 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
