PHYLUM PROTOZOA 



43 



bearing a single zooid or a group of zooids at the end of 

 each of the branches (Fig. 14, J), the whole colony being 

 fixed by the base of the main stalk, and the flagellum serving 

 for the capture of food-particles and not for locomotion. 



Fig, 17. — Volvox globator. A, entire colony, enclosing several daughter-colonies; 

 B, the same during sexual maturity: C, four zooids in optical section; D 1 — D 5 , 

 asexual formation of daughter-colony; E, zooid which has become converted 

 into a mass of microgametes; F, microgamete; G, megagamete surrounded by 

 microgametes; H, zygote; a, early stages in the formation of daughter-colonies; 

 fl, flagellum; ov, ovy, megagametes; f>g, pigment spot; spy, zooids containing 

 microgametes. (From Parker's Biology, after Cohn and Kirchner.) 



Sometimes (Fig. 17) the colony is of a more massive char- 

 acter, the zooids being embedded in a clump of gelatinous 

 material, with the end bearing the flagellum projecting on 

 the exterior : usually such colonies are free-swimming. 



