54 



THE INVERTEBRATA 



gametes are considerably modified, being pale, very slender, and 

 bearing their flagella in the middle of their length. Male, female, and 

 asexual reproductive zooids may be found in any combination in a 

 colony. Details of the structure of the colonies are shown in Figs. 45, 46. 



Vc..£ 



V4£. 



Fig. 45. Diagrams to show the structure of the colony of two species of Volvox. 

 After Janet. V.a.i. Surface view of a small part of the colony of V. aureus. 

 V.a.2. Section through a similar region, V.g.i. and V.g.2. show V.globator in 

 the same way. The zooids are very different in shape in the two species, but in 

 both they have been separated by the formation of mucilage (mw) by the cell- 

 walls; the unaltered middle layer of the walls {m.L) is still visible. Proto- 

 plasmic strands (p.c), fine in the one species and thick in the other, connect the 

 zooids. Otherwise each zooid, with its single curved chloroplast (ch), eye-spot 

 and two flagella, has the structure of a Chlamydomonas . 



Subclass ZOOMASTIGINA 



Mastigophora which do not possess chromatophores and are not 

 otherwise practically identical with coloured forms. 



By one or more of the following peculiarities of the Zoomastigina 

 most members of the group are distinguished from most colourless 

 members of the Phytomastigina. 



