MASTIGOPHORA: FLAGELLATA. 845 



The Dendromonads are grouped singly or in numbers at the ends of a 

 branching solid stem ; the Spongomonads Cladomonas and Rhipidodendron 

 at the ends of branching tubes, whilst the individuals of Uroglena, Symira, 

 and Spongomonas are enveloped in a jelly-like mass, and in the first two 

 may or may not be connected at its centre. In Syncrypta the envelopes 

 of the zooids are united at a common centre ; in the Volvocina they are 

 contained by a common investment. The number of individuals in a 

 colony varies from a few, e.g. 4-16 in Gonium, 16 in Pandorina, 32 in 

 Eudorina, to as many as 12,000 in Volvox globator. Each individual may 

 undergo repeated binary fission within its own envelope to form a new 

 colony which is set free ; or, as in Volvox, this power is restricted to certain 

 large non-flagellate individuals, the parthenogonidia, always few in number, 

 e. g. eight in V. globator. Every individual in Volvox is connected to each 

 of the six individuals immediately surrounding it by a protoplasmic thread. 

 The colonies of Eudorina and Volvox are hollow. 



Permanent conjugation has been observed in some Monads, in Bodo, 

 in Chlamydomads (except Haematococcus and Coccomonas}, and in Vol- 

 vocina. In small species of Monads and Bodo several individuals may 

 become amoeboid, then non-flagellate, and fuse into a plasmodium, which 

 encysts and undergoes repeated fission. In other instances a partially 

 amoeboid stage may supervene, the individuals fusing in pairs, at first only 

 by their hinder extremities ; or if not amoeboid, they may differ in size, 

 points of structure, and life-history. The contents of the cyst may give rise 

 to minute flagellate individuals (zoospores), or to a more or less granular 

 fluid, the granules of which are said to grow into flagellate individuals, 

 e.g. in Dallingeria. The Chlamydomonads have as a rule small indi- 

 viduals or microgonidia, which either fuse one with another in pairs or 

 a microgonidium with an ordinary individual (macrogonidium). The two 

 unite by their anterior ends, their envelopes dissolving at this point. The 

 flagella and stigmata are eventually lost and the zygote or zygospore 

 becomes rounded and encysts, a formation of haematochrome taking place 

 in green-coloured species. Further development generally takes place only 

 after the zygote has been dried for a time, or, in Polytoma, has been 

 transferred to a fresh infusion. Two or four individuals are then formed 

 by fission. In Carteria, however, a Pleurococcoid condition has been 

 observed (ante, p. 844). As to Volvocina there appears to be a con- 

 jugation of microgonidia in both Gonium and Stephanosphaera. In 

 Pandorina each individual gives origin to a colony of eight. The parent 

 colony, now motionless, sinks ; its coat and the coats of the original 

 individuals slowly soften and gelatinise. The cells in each colony of eight 

 acquire a transitory common coat and cilia. They are eventually set free, 

 and conjugate in pairs. A difference of size in the conjugating individuals 

 is said to be noticeable. This difference is much more marked in Eudorina 



