THE GREEN CELLS OF CONVOLUTA IfOSCOFFENSlS. 191 



borne at the ends of branching gelatinous stratified stalks. 

 This habit occurs, according to Oltmanus (1904), in other 

 genera of the Chlamydomouadea3, viz. Chlorangium (Stein), 

 and Pliysocytiuni (Borzi). The nearest approach, howevei-, 

 to this habit of the infecting alga is exhibited by species of 

 the genus Prasiuocladus of the family Chlorodendracete, 

 which stands, according to Oltnianns, between the Chlamydo- 

 monadeaB and the Polyblepharideas. 



We conclude that the infecting organism is a true alga 

 and a primitive member of a primitive group, the Chlamydo- 

 monades); and that whilst presenting many features cha- 

 racteristic of the genus Carteria, its possession of certain other 

 charactei's, facultative gametes, branching as well as plate- 

 like colonial form and its lack of contractile vacuoles, makes 

 its assignment to that genus doubtful. 



Summary of Section IV. 



The infecting organism of Convoluta is an alga belonging 

 to the Chlamydomonadea3. 



In its free stage it bears four equal flagella and possesses 

 the general characters of members of this family. 



The active cells are of two sizes, but neither large nor small 

 cells appear to be obligate gametes. 



The organism is capable of a saprophytic as well as of a 

 holophytic existence ; in the former state it may be colour- 

 less. 



The active cells are attracted chemotactically to egg- 

 capsules of Convoluta. They settle down and undergo active 

 vegetative division in the capsules, and are finally liberated 

 as a swarm of four-flagellated active cells. 



Section V. The Normal Course of Infection. 



We have demonsti-ated in Section III that the active 

 flagellated cells of the infecting alga may be ingested by 

 Convoluta and, dividing in the body of the animal, give rise 

 to the green-celled " tissue" characteristic of the adult. 



