REPRODUCTION, 



55 



plex ones, involving throughout the process of oxidation ; for 

 it must ever be kept in mind that life and oxidation are con- 

 comitant and inseparable. The further study of reproduction 

 in the concrete will render the meaning and force of many of 

 the above statements clearer. 



THE OVUM. 



The typical female cell, or ovum, consists of a mass of pro- 

 toplasm, usually globular in form, containing a nucleus and 

 nucleolus. 



The ovum may or may not be invested by a membrane ; the 

 protoplasm of the body of the cell is usually highly granular, 

 and may have stored up within it a varying amount of proteid 

 material (food-yelk), which has led to division of ova into 

 classes, according to the manner of distribution of t^s nutri- 

 tive reserve. It is either concentrated at one pole (telohcith- 

 al) ; toward the center (centrolecithal) ; or evenly distributed 

 throughout (alecithaT). 

 During development this "^ 



material is converted by ""^-^ 

 the agency of the cells of 

 the young organism (em- 

 bryo) into active proto- 

 plasm ; in a word, they 

 feed upon and assimilate 

 or build up this food-stuff 

 into their own substance, 

 as Amoeba does with any 

 proteid material it appro- 

 priates. 



The nucleus (germinal 

 vesicle) is large and well 

 defined, and contains with- 

 in itself a highly refractive 

 nucleolus (germinal spot). 

 These closely resemble in general the rest of the cell, but stain 

 more deeply and are chemically different in that they contain 

 nucleine (nucleoplasm, chromatin). 



It will be observed that the ovum differs in no essential par- 

 ticular of structure from other cells. Its differences, are hidden 

 ones of molecular structure and functional behavior. In ac- 



FiG. 55. — Semi-diagrammatic representation of 

 a mammalian ovum (Schaf er). Highly mag- 

 nified. 2^, zonapellncida; vi, vitelms (yelli;); 

 gv, germinal vesicle; gs, germinal spot. 



