THE MASTIGOPHORA 173 



individuals appear to be facultative gametes and there is no sexual 

 differentiation. During the conjugation the nucleus of each of the 

 conjugants divides at least once, one of the daughter nuclei thus 

 produced, being a polar nucleus, degenerates in the cytoplasm and 

 is lost. The remaining nucleus of each conjugant fuses with its 

 fellow to form the nucleus of the zygote. It should be stated that 

 after the first division of the nuclei of the conjugants small granules 

 of chromatin are protruded from the central chromatin mass and 

 are lost in the cytoplasm (heteropolar division). The zygote 

 behaves exactly like an ordinary individual and divides soon after 

 it is formed by longitudinal fission in the ordinary manner. 



ORDER 3. Chrcmomonadidea. 



This is the first of the groups of Mastigophora that are regarded 

 by many authors as belonging to the vegetable kingdom ; for, 

 although there is an active free- swimming stage of life, the method 

 of nutrition appears to be in all cases holophytic. In the Chloro- 

 monadina, which may be regarded as in many respects intermediate 

 between this order and the other Lissoflagellata, there is a funnel- 

 shaped depression at the base of the flagellum ; but this does not 

 serve the purposes of a mouth, but is an excretory duct of the 

 contractile vacuole reservoir. In the other tribes of the order 

 even this vestige of the Lissoflagellate mouth is lost. The Chloro- 

 monadina also resemble the Euglenoids in having the chlorophyll 

 scattered through the endoplasm in minute chloroplasts. No 

 process of conjugation has yet been observed in this order. Among 

 the Chrysomonadina, Chrysamoeba has the ordinary form of a 

 flagellate organism when it is actively swimming, but when it 

 comes to rest it protrudes delicate radiating pseudopodia and 

 resembles a Mastigamoeba. 



Chromulina rosanoffi, according to Woronin (23), forms a scum of 

 encysted individuals at the surface of ponds in Finland. This 

 gives rise to the flagellate swarm-spores which after a time penetrate 

 the cells of Spirogyra and again encyst. In Dinobryon the indi- 

 viduals are attached to the base of an open receptacle. They 

 usually occur in dense spreading free-swimming colonies (Fig. 5 (8)). 

 Reproduction is by fission or by the formation of spherical cysts 

 which escape from the receptacle and start new Dinobryoid colonies. 

 Syncrypta (Fig. 5 (4)) forms globular colonies invested by a 

 mucilaginous test through which the flagella protrude. Uroglena 

 also forms globular colonies, but the flagellate individuals are at the 

 periphery and the centre is filled with mucilage. 



The genera comprised in this order are freshwater in habit, 

 except the Coccolithophoridae, which are exclusively marine. 



The order is divided into three tribes : 



