THE PHYSICAL BASIS OF HEREDITY. 167 
reproductive cells is found in Volvox globator. This form , 
consists of a hollow spherical colony of as many as 
twenty-two thousand cells placed in a 
single layer in a hyaline jelly-like sub- 
stance, and connected with each other by cytoplasmic 
processes. Each one of the cells is a somewhat ovoid 
Volvox. 
Fic. 8.—Zudorina elegans,a female colony around which antherozooids 
are swarming: A, cluster of antherozooids still united ; B, cluster 
of antherozooids just separating ; C, swarming antherozooids, some 
of which have already penetrated into the female colony D. (After 
Goebel.) 
mass of green-coloured protoplasm, and bears two long 
cilia upon its outer, pointed, hyaline end which project 
out into the water and, lashing to and fro, give to the 
whole colony a rotary motion. At'the time of reproduc- 
tion, certain cells of the colony undergo profound modi- 
fications. Some of them increase in size enormously, 
having reserve food material stored up in them, and 
become the egg cells or oospheres. Other cells divide 
