54 ANIMAL PHYSIOLOGY. 
is termed by the biologist development, but which may be ex- 
pressed by the physiologist as the transformation of potential 
into kinetic energy, or the energy of motion. Viewed chemic- 
ally, it is the oft-repeated story of the production of forms, of 
greater stability and simplicity, from more unstable and com- 
plex ones, involving throughout the process of oxidation ; for it 
must ever be kept in mind that life and oxidation are concomi- 
tant 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 proto- 
plasm, usually globular in form, containing a nucleus and nu- 
cleolus. 
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 this nutri- 
tive reserve. It is either concentrated at one pole (telolecith- 
al); toward the center (centrolecithal) ; or evenly distributed 
throughout (alecithal). Dur- 
ing development this material 
is converted by the agency of 
the cells of the young organ- 
ism (embryo) into active pro- 
toplasm; in a word, they feed 
upon and assimilate or build 
up this food-stuff into their 
own substance, as Amceba does 
with any proteid material it 
appropriates. 
The nucleus (germinal vesi- 
cle) is large and well-defined, 
Fie. Pee aerate F_ pusseutation and contains within itself ao 
Cana a cram Gcnéfer). Muebly highly refractive nucleolus 
Hs Sty. germinal vestele gr, wenninal (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- 
