30 



THE INVERTEBRATA 



The fate of flagella at fission varies. Sometimes, as in Chlamy- 

 domonas and Polytoma^ they are lost, early or late in the process. In 

 other cases they are retained. When this happens in an organism with 

 a single flagellum, that organ has been said sometimes to be split 

 longitudinally, but usually, if not always, a second flagellum grows 

 out from the basal granule, which divides. When several flagella are 

 present and persist, they are distributed between the ofi^spring, each 

 of which grows new flagella to complete its equipment. Probably, 

 a new flagellum always grows from a basal granule. Chromatophores 

 divide, and if numerous may do so independently of the fission of the 



Fig. 24. Polytoma uvella, x about 1300. A, Ordinary individual, showing 

 nucleus, eye-spot, contractile vacuoles, flagella with basal granules, and 

 starch grains, the latter confined to the hinder part of the body. B-E, stages 

 of the first fission. In C and D the flagella are omitted. After Dangeard. 



body. Contractile vacuoles and other organs rarely (Euglena) divide, 

 but are usually shared as the flagella. Complex organs, however, are 

 often destroyed (dedifferentiated) and remade by the individual that 

 receives them. 



Conjugation^ or syngamy,^ the union of two nuclei, accompanied by 

 the fusion of such cytoplasm as each may possess, is, so far as our 



^ The name conjugation is by some authorities restricted to the peculiar 

 process by which syngamy is accomplished in most ciliophora (p. 33). 



^ The union of nuclei is karyogatny : in most cases of syngamy it is accom- 

 panied by plasmogamy or the fusion of cytoplasm, but in typical ciliophora 

 one of each pair of fusing nuclei has perhaps no cytoplasm ; and autogamy 

 (p. 33) is said sometimes to occur between nuclei whose cytoplasm has never 

 been divided. Plastogamy (p. 36) is plasmogamy without karyogamy. 



