100 THE CELL DOCTRINE. 



nuclei make their appearance. This is known as 

 genesis. It is the second and most frequent mode of 

 the formation of anatomical elements. It is char- 

 acterized by. the appearance of an anatomical ele- 

 ment in 'a fluid termed blastema, in which the 

 element did not previously exist. 



3d. Epige.nesis. — When the embryonic cells dis- 

 solve, the embryo -plastic nuclei are produced by 

 genesis in the blastema which results from their 

 fusion. Then little cone-like prolongations of trans- 

 parent matter are observed at the extremities of the 

 nuclei, giving rise to the fusiform bodies, which are 

 the connective tissue corpuscles. This mode of forma- 

 tion by growth upon another element is known as 

 epigenesis, and is the mode in which connective tissue 

 is developed. The prolongations of these fusiform 

 bodies constitute the non-elastic fibres or white 

 fibrous tissue element of connective tissue. Some- 

 times the substance deposited by epigenesis upon the 

 nucleus has several prolongations, forming a stellate 

 cell or connective tissue corpuscle. These fusiform 

 and stellate cells are likewise known as emhrgo-jylastio 

 ov fibro -plastic bodies, and this latter term is a most 

 common one in French histology. 



The elastic fibres of connective tissue are likewise 

 formed by epigenesis, but upon special nuclei, and 

 the prolongations are insoluble in acetic acid. 



There is an early period of foetal life, previous to 

 the formation of connective tissue, in which we find 

 only embryo-plastic nuclei and fusiform bodies in 

 amorphous matter. This is called embryo-plastic 

 tissue. Growth at this epoch is most rapid, the 



