VOLVOCINA 



SI 



domonas in that there is a wide space, traversed by protoplasmic 

 threads, between body and cuticle; several pyrenoids. Much hae- 

 matochrome is often present. Isogamous. Common in collections 

 of rainwater. 



Pandorina (Fig. 43). Spherical, free-swimming colonies of 16 or 

 32 pear-shaped zooids, each with the organization of a Chlamy do- 

 monas, closely pressed together with the narrow end inwards and the 



Fig. 41- 

 Fig. 41. Noctiluca, x 65. A, Ordinary individual. B, Spore formation. 

 C, A spore. After various authors, with modifications, fl. flagellum; nu. 

 nucleus; ten. tentacle; tth. tooth. 



Fig. 42. Haematococcus lacustris, x 475. From West. A-C, Individuals in 

 ordinary phase, showing strands of protoplasm from body to cuticle. D, F, E, 

 Successive stages in fission. G, H, Individuals in resting phase. 



flagella outwards. An additional cellulose envelope containing mucilage 

 encloses the whole colony. The colonies are reproduced in two ways : 

 (i) asexually, by the repeated fission of each zooid to form a group of 

 16 like the parent colony, the dissolution of the colonial and zooid en- 

 velopes, and the setting free of 16 young colonies ; (2) sexually, by the 

 division of each zooid and the setting free of its products as gametes 

 which, except in size, resemble ordinary zooids. Since the number 

 of fissions in the formation of gametes differs in different colonies, 



4-2 



