i8o THE MASTIGOPHORA 



of the most primitive of the Chlorophyceous Algae. The principal genera 

 are Palmella, Lyngbye ; Palmodactylon, Nageli ; Sphaerocystis, Chodat ; 

 Schizochlamys, A. Br. ; Tetraspora, Link ; Apiocystis, Nageli ; Gloeocystis, 

 Nageli ; and Palmodictyon, Kiitzing. 



ORDER 1. Chlamydomonadina. 



Solitary forms in the flagellate phase. 



In Chlamydomonas, which may be taken as an example of this 

 order, there are two flagella in the free-swimming stage, the body 

 is enclosed in a cellulose investment, there are two small contractile 

 vacuoles at the anterior end, a stigma (eye-spot), a single nucleus, 

 and one or more pyrenoids. Two individuals may conjugate and 

 form a zygote. The zygote encysts, the flagella being lost, and 

 the protoplasmic contents divide into as many as sixty-four cells 

 (Fig. 5 (3)); these cells escape as flagellate individuals similar in 

 general characters to the gametes, but instead of conjugating they 

 form a gelatinous investment, lose their flagella, and divide repeatedly 

 (the "palmella- stage"). From the gelatinous investment of the 

 colony that is thus formed the flagellate gametes ultimately escape. 

 Reproduction may also occur by the formation of a resting cyst and 

 the division of the cell-contents into two, four (Fig. 5 (2)), or eight 

 cells, which escape in a form like the parent. 



The introduction into the life-history of this genus of a non- 

 flagellate " palmella-stage " during which growth and reproduction 

 take place has suggested that Chlamydomonas " is the phylogenetic 

 starting-point of the various lines of Chlorophyceous descent" 

 (Blackmail and Tansley). That there is a strong resemblance 

 between the swarm-spores of many Algae and flagellate forms such 

 as Chlamydomonas cannot be denied, but the conclusion that all the 

 green Algae are descended from a flagellate ancestry is not universally 

 accepted (see West [22], p. 33). 



Sphaerella, Sommerfeldt, 1824, is probably the correct generic name 

 for a very abundant organism found in rain-pools, water-butts, etc., that 

 is sometimes called Haematococcus, Agardh ; Chlamydococcus, Braun ; or 

 Protococcus, Huxley and Martin. The individuals may become brick-red 

 owing to the presence of " Haema,tochromin," and give rise to the 

 phenomena known as " red rain " and " red snow." The structure and 

 life-history of this organism are very similar to that of Clilainydomonas. 

 The infecting organism which forms the green ceils in the Turbellarian 

 worm Convoluta roscoffensis is, according to Keeble and Gamble (7), a 

 Chlamydomonad allied to Garteria. 



The principal genera are : 



Carteria, Diesing, with four flagella ; Chlamydomonas, Ehrenberg ; 

 Sphaerella, Sommerfeldt (Fig. 5 (9, 10)) ; Haematococcus, Agardh ; Polytoma, 

 Ehrenberg (Fig. 7 (8)) ; Chlorogonium, Ehrenberg (Fig. 5 (6)) ; Pyramimona*, 

 Schmarda. 



