THE ALGAE 



67 



Volvox 



In Volvox we have the largest colony of this type which is known (Fig. 

 44). It consists of a hollow sphere or ellipsoid of up to 20,000 cells, forming 





■•■ '■ •/ 



*.%.;:#•,■,"-.-.■%'.. • .• • :_ ■ • ■■-■•*.':* ••■J 



Large oosphere 



Young oosphere 

 Vegetative cells 



Fig. 44. — Volvox aureus. Entire mature colony in surface 

 view showing vegetative and reproductive cells. 



a peripheral layer within the mucous sheath (Fig. 45). The individual cells 

 are of the general chlamydomonad type, with globose, oval or stellate 



Vegetative 

 cells 



Gonidium 



\ By courtesy of the Biological Supply House Inc . , Chicago, U.S. A . 



Fig. 45. — Volvox aureus. Detail of the colony surface in transverse section 

 showing the layer of vegetative cells and an enlarging gonidium. 



chloroplasts, often with several contractile vacuoles and one or more 

 pyrenoids. The cell walls are thick and gelatinous, often with a firmer 

 middle lamella which forms a polygonal pattern between the cells. The 

 cells of the colony are connected together by means of protoplasmic strands. 

 These may be very slender, but in Volvox globator they are thick processes 



