EUPHYCOPHYTA 



29 



of a sphere with 500-60,000 biflagellate cells set around the peri- 

 phery, the flagellae emerging through canals. The actual number 

 of cells in a colony varies from species to species. The interior of 

 the colony is mucilaginous (e.g. V. aureus) or else merely contains 

 water (e.g. V. globator), whilst the entire collection of generally 

 ovoid cells is bounded on the outside by a firm mucilaginous wall. 

 The individual cells, each containing two to five contractile 



Fig. 8 Volvox. A,V. aureus with daughter colonies. B, structure of 

 V. aureus as seen in section. C, surface view of single cell of V. 

 rousseletii ( x 2000). D, the same in side view ( x 2000). (A, B, after 



Fritsch; C, D, after Pocock.) 



vacuoles, in some species are surrounded by distinct individual 

 sheaths, the middle lamellae of which form a polygonal pattern 

 when stained with methylene blue. In some species too the cells 

 are united by deHcate cytoplasmic threads, or plasmodesmae. In 

 V. glohator and V. rousseletii the cells are *sphaerelloid' in nature, 

 each individual cell being enclosed in a separate envelope, whilst 

 in V. aureus a number of individual chlamydomonad cells are en- 

 closed in wedge-shaped prisms, which morphologically may be 

 equivalent to an original mother cell. It has therefore been sug- 



