Carter ie& 



close contact with the protoplast. This character, and the presence of only 

 two contractile vacuoles 1 situated at the anterior end of the cell close to the 

 base of the cilia, are the leading distinctions between the Volvocaceaj and the 

 Sphaerellacea3. In the majority of forms the chloroplast contains only one 

 pyrenoid, although several normally occur in Chlamydomonas giganteus Dill 

 and Pleodorina illinoisensis Kofoid ; and Bachmann ('05) has occasionally 

 observed two or three pyrenoids in specimens of Chlamydomonas inJuvrens. 



In the few forms included in the Carterieae (the Carteriacese of Pascher) 

 the cells are furnished with four cilia. 



Sul>-fain. Carteriese. 



genera of this sub-family possess four 



The Volvocacese may be ,sul)divided as follows : 



A. Cells with four cilia ; unicellular or coenobic. 



B. Cells with two cilia. 



a. Unicellular. 



*Cell-wall thin but distinct. Sub-fain. Chlamydomonadeae. 



**Cell-wall firm and often thick, .sometimes consisting of two loosely con- 

 nected halves. Sub-fain. Phcicntese. 



b. Cells aggregated to form cu-nobia with very definite characters. 



Sub-fain. 



Sub-family CARTERIE^:. All the 

 equal cilia attached to the anterior 

 end of the cell. The principal genus 

 is Carteria, in which the cells are 

 spherical, ovoid or ellipsoid, and pro- 

 vided with a thin cell-wall. Near the 

 attachment of the cilia are two small 

 contractile vacuoles; and a conspicuous 

 pigment-spot is present, although its 

 position is variable. The chloroplast 

 is large and massive, hollowed out 

 anteriorly into the form of a basin or 

 cup, and is usually furnished with a 

 single conspicuous pyrenoid in its pos- 

 terior thicker part (fig. 98 A and B). 

 The presence of four cilia is the only 

 feature distinguishing this genus from 

 Chlamydomonas. In the formation 

 of zoogonidia the first division-plane 

 is longitudinal or slightly oblique. 

 In several species quadriciliated 

 isogametes are also known, which 



K 



ft- 1 



H ' I 



Fig.98. A G,Carteri,t 



A and B, vegetative cells ( = zoogonidia) ; C, 

 four daughter-cells within old wall of mother- 

 cell; D, gametes; E, conjugating gametes; 

 F, zygote. H and /, Chlamydomonas Debary- 

 ana Gorosch. J and K, Chi. grandis Stein 

 (=Chl. Kleinii Schmidle). All x 475. cr, con- 

 tractile vacuoles; n, nucleus; p, pyrenoid; 

 zg, gamete; z, zygote. 



1 In Aijloe there is an additional group of three contractile vacuoles at the posterior end of 

 the cell (vide Pascher, '12). 



