190 F. KEEBLK AND V. W. GAMBLE. 



monadeas ; uiid the possession Ly the cells of four HageUa 

 would indicate tlie genus Carteria. 



Nevertheless we would wish to assign it only provisionally 

 to this genus for the following reasons : 



First, the infecting alga never lias contractile vacuoles, two 

 of which are described in the known species of Carteria. 



Second, though like some species of Carteria — e. g. 

 C. niultifilis (Fresen) — it possesses cells of two sizes (West, 

 1904); yet, Avhereas in C. niultifilis the small cells are 

 gametes and the large, vegetative cells, neither the large nor 

 the small cells of our organism appear to be obligate 

 gametes. Numerous experiments which we have made of 

 bringing together microcytes from different cultures, micro- 

 cytes and macrocytes, and macrocytes from different cultures 

 have given but meagre and extremely rare evidence for any 

 sexual fusion. Leaving aside as unexplained the phenomenon 

 already described in which one of a pair of resting-cells 

 gradually decreases in size and finally disappears, we have 

 only once obtained evidence of what may be a gametic union. 

 PI. 14, fig. 11 D, shows the case in point. Here two motile 

 cells have come together, their Avails have united, and the 

 cells appear in process of fusion. 



If this be a true case of sexual fusion, it presents features 

 of great interest. For, as Blackmail (1900) has pointed out, 

 the Chlamydomonadea3 exhibit a remarkable series of modes 

 of gametic fusion. In some forms the walls are thrown off 

 whilst the gametes are approaching one another, in others 

 at the moment of meeting. In Chlamy doni onas niulti- 

 filis, a four-ciliate form, partial fusion takes place first, so 

 that the walls are left fused at one spot. Blackman adds 

 that the series might be completed at its lower end by a 

 form which fused without losing its walls. The figure just 

 referred to appears to indicate that this primitive form of 

 sexual union is exhibited by the infecting alga of Coiivoluta. 



A third character which seems to separate it from Carteria 

 is the peculiar branching habit which it sometimes presents. 

 lu this condition (PI. 13, fig. 8) inverted green cells are 



