A GERM-CELL CYCLE IN ANIMALS 
wise have taken place in the Cell Theory; we no 
longer consider cells as isolated units and the multi- 
cellular animal as equivalent to the sum of its con- 
stituent cells, but recognize the influence of the cells 
upon one another, thus reaching the conclusion that 
the metazoén represents the sum of the individual 
cells plus the results of cellular interaction. 
Cells vary considerably in size, ranging from those 
we call Bacteria, which may be no more than 33459 
of an inch in length, to certain egg cells which are 
several inches long; the latter, however, owe their 
enormous size to the accumulation of nutritive sub- 
stances within them. An average cell measures 
about gz55 of an inch in diameter. Cells vary in 
shape as well as in size; egg cells are frequently 
spherical, but most cells are not, since they are sur- 
rounded by other cells which press against them. 
A diagram of a typical cell is shown in Fig. 1. 
Authorities are not agreed as to the structure of 
protoplasm; to some it appears, as shown in Fig. 1, 
to consist of a network of denser fibers called spon- 
gioplasm (s) traversing a more liquid ground 
substance, the hyaloplasm. Others consider proto- 
plasm to be alveolar in structure, thus resembling 
an emulsion, whereas another group of zodlogists 
maintain that while protoplasm may appear to be 
fibrillar or alveolar, its essential basis consists of 
multitudes of minute granules. Wilson’s view is 
the one usually adopted at the present time; that 
is, the protoplasm of the same cell may pass suc- 
cessively ‘“‘through homogeneous, alveolar, and 
