GENERAL EMBRYOLOGY 1597 



GENERAL EMBRYOLOGY. 



Embryology is a treatise on the embryo and the development of 

 its tissues and organs from the stage of the fertilized ovimi to their 

 mature condition. 



Two factors are concerned in the formation of the embryo — 

 namely, (i) the male pronucleus, formed by the head and a portion 

 of the middle piece of a spermatozoon or male germ-cell, and (2) the 

 female pronucleus, which represents the mature ovum or female 

 germ -cell. 



The Animal Cell. 



The animal cell is a mass of a living substance called protoplasm. 



The essential component parts of the cell are (i) a cell-body, and 

 (2) a nucleus. The nucleus may contain one or more nucleoli, but 

 these are not essential elements. The protoplasm of the cell-body 

 is called the cytoplasm, or cell-protoplasm, and it may be enclosed 

 (as in the ovum) within an envelope, called the cell-membrane, which 

 is simply a condensation of the peripheral cytoplasm. The proto- 

 plasm of the nucleus is called 



the karyoplasm, or nucleoplasm, ^^-s"!^?:;!?^??;^^ Centrosome 

 and it is enclosed within an /^'^^^v-v'H^y^^^^ 

 envelope, called the nuclear /' '" ' ' ' ''^ ' ■ >v '*'"^'°* 

 membrane. The animal cell is - .>-4:' >\ 

 therefore 'a mass of proto- ■ .^ ' '^^ 

 plasm, containing a nucleus.' ^ ■;'=": Karyoplasm 



Cytoplasm. — The cytoplasm ^ , • x ". >^^^ ''^" ' t -^ l{"^ 

 is the protoplasm of the cell- y -7 " ' ;>' ^-'i *°"* 



body, as distinguished from the \-^>*(, . >'' v ^ 



karyoplasm, which is the proto- ^ '•, -^, ; ^ " ' ' " 

 plasm of the nucleus. It is /^ ^^ 1^^^ 



viscid, translucent, and more or ^^^^^ 



less granular. At the periphery Fig. 656. — The Animal Cell. 



it may be condensed to form a 



cell-membrane. The basis of the cytoplasm consists of a network 

 of slender filaments, which is known as the sfongioplasm. The 

 meshes of this reticulum are occupied by a semifluid substance 

 called the hyaloplasm. 



The cytoplasm contains granules, which are called cyto-micro- 

 somes. The hyaloplasm, in addition to the cyto-microsomes, con- 

 tains several non-protoplasmic bodies — e.g., food-particles and 

 pigment-granules — which are known as the dentopiasm. 



