306 



THALLOPHYTES 



vitally related that the colony of Volvox may be regarded as a 

 multicellular individual rather than a colony. 



Reproduction presents some interesting features. At first all 

 cells of the colony are alike, but later considerable differentiation 

 among cells occurs. Some cells of the colony enlarge and pass 



FIG. 261. Volvox. In the colony (Volvox aureus) the smaller cells bear- 

 ing two cilia are the vegetative cells, the enlarged cells (a) contain sperms, 

 and the enlarged cells (o), varying in size and stages of development, are 

 eggs (X 300). Below and at the right is a sperm, and below and at the 

 left is a oospore of Volvox globator. After West. 



into the hollow of the sphere where they form new colonies which 

 escape and grow to adult size. Sexual reproduction in Volvox 

 is heterogamous, for two distinct kinds of gametes are involved. 

 Some of the cells enlarge, lose their cilia, and become filled with 

 food. They are the female gametes or eggs. Other cells of the 

 colony form numerous small motile gametes or sperms which seek 

 the eggs and fuse with them. Fertilization, as this fusing is 

 called since the gametes are differentiated into eggs and sperms, 



