78 THE PROTOZOA 



in a complicated manner. In the remarkable Acinetan Dendrosoma 

 radians a colony is formed by budding, which resembles super- 

 ficially a hydroid colony, each hydranth being represented by the 

 head of an Acinetan individual with suctorial tentacles ; the 

 branched nucleus is continuous throughout the whole colony, pass- 

 ing uninterruptedly from one individual to another. 



Typically the cell-body contains a single nucleus, but in many 

 Protozoa two or more nuclei occur constantly. When there are 

 more nuclei than one, they may be all alike 

 and quite undifferentiated, or they may show 

 differences in size, structure, and function. 

 In many Sarcodina multiple nuclei without 

 differentiation are found to occur constantly 

 in certain species ; for instance, two in Amoeba 

 binudeata and Arcdla ; several, perhaps a 

 dozen or so, in Difflugia (Fig 16) ; from 

 twenty to forty up to some five hundred in 

 Actinosphcerium (Fig 3) ; so also in Pdomyxa ; 

 and in the large plasmodia of Mycetozoa many 

 thousands of nuclei are found. 



Differentiation of nuclei, when it occurs, 

 may be related to various causes. In trypano- 

 somes and allied forms two nuclei occur con- 

 stanfcl y a principal nucleus, or tropkonudeus, 

 (Esox lucius). so called because it appears tjo regulate the 

 a.fl., Anterior flagel- general metabolism and trophic activities of 



lum; n, kinetonu- 7, ., , , ., , . , . , . . 



cleus ; N, trophonu- the cell- body ; and a kinetonudqus, which is in 



cleus;p./Z., posterior special relation to the organs of movement, 



I^t*2 fla 8 ella > and undulating membrane. As a rule 



ting membrane, and the kinetonucleus is smaller, in some cases very 



continued beyond it minute an( i nas a dense compact structure, 



as a very short free ' 



flagellum posteriorly, while the trophonucleus has a vesicular struc- 



ture ' k ut m otiier cases ( Tjr yP an P lasma ) the 

 kinetonucleus is the larger of the two (Fig. 36). 



A nuclear differentiation of totally opposite character is seen 

 in the Infusoria, where two nuclei of different sizes, hence termed 

 " macronucleus " and " micronucleus," are constantly present ; the 

 behaviour of these two nuclei in relation to sexual phenomena and 

 reproduction (vide p. 153, infra) shows that the macronucleus is 

 composed of vegetative chromatin, while the micronucleus contains 

 the reserve generative chr.omatin. In some cases for example, in 

 Myxosporidia (p. 403) nuclei of different sizes occur in relation to 

 sexual differences. 



In some Protozoa the so-called " Monera " of Haeckel the 

 nucleus has been stated to be wanting entirely ; but this statement 



