Volvocaeete 187 



become rounded and repose in a copious mass of mucilage. 

 Akinetes are also known to occur. 



Sexual reproduction occurs by the conjugation of isogamous 

 or heterogamous planogametes, which are smaller but otherwise 

 similar to the vegetative individuals. They arise as do the latter 

 by the division of the contents of a mother-cell, but as many as 

 64 may be produced in one cell. 



A. Vegetative cells with 4 cilia Carteria. 



B. Vegetative cells with 2 cilia. 



* Cell- wall thin, closely adherent. 



t Cells spherical, ovoid, or ellipsoid, rarely 

 fusiform ; chloroplast definite, with one 



pyrenoid Cklamydomonas. 



tt Cells fusiform, 3 or more times longer than 

 the diameter ; chloroplast indefinite, with 



t\v< > or more pyrenoids C-h lorogonium. 



** Cell-wall thin, outstanding and connected by 



protoplasmic threads Sphcerella. 



Genus Carteria Diesing, 1868. [Pithiscus Dang., 1888; Cor- 

 biera Dang., 1888.] The cells are spherical, ellipsoid, or cordiform, 

 with a bell-shaped chloroplast containing a single large pyrenoid. 

 There is a prominent pigment-spot towards the anterior end of 

 the cell, and there are four cilia. The only distinction between 

 this genus and Chlamydomonas is the presence of four cilia instead 

 of two. 



C. multiflis (Fresen.) Dill is a fairly abundant species in small pools, more 

 particularly of rain-water. Diam. vegetative cells 1016 p. (fig. 73 A G). 



Genus Chlamydomonas Ehrenb., 1833. The vegetative cells 

 are of variable size, spherical, ovoid, oblong-ellipsoid, or pyriform, 

 and the anterior end is often slightly produced to form a small 

 beak or rostrum to which are attached two cilia. The cell-wall is 

 hyaline, often very indistinct, and is closely adherent to the cell- 

 body. The chloroplast is very variable in form, and is usually 

 furnished with a single pyrenoid (rarely entirely without or with 

 several pyrenoids). There are two (rarely mote) contractile vacuoles 

 in the anterior region of the cell, and generally a pigment-spot. 

 The reproduction is typically that described for the sub-family, 



and the wall of the zygospore may be smooth or asperulate. 



.*- 



There are about 29 known species of the genus, but the characters of some 

 of them are not clearly evident. Little work has been done at the British 



