394 THE INFUSORIA 



If, however, in such an animal the limits of somatic and germinal 

 cytoplasm were indistinguishable (Fig. B), we should have an 

 organism precisely similar in its essential features to one of the 

 Heterokaryota, and just as the hypothetical form is strictly 

 bicellular or tricellular, so is the Heterokaryote, strictly speaking, 

 not unicellular, but bicellular or tricellular, etc., according to the 

 number of micronuclei it possesses. 



The matter is, however, to a certain extent a question of 

 nomenclature. If it is considered to be desirable to include in the 

 term, "cell," everything that is enclosed by the outline of a cyto- 

 plasmic unit, then the Heterokaryota may be called unicellular ; 

 but the definition of a cell must be extended so as to include 

 examples in which the cytoplasm includes nuclei of two or more 

 distinct characters. 



The differences between the meganucleus and the micronucleus 

 in the Heterokaryota are very pronounced. 



PIG. A. Fio. B. 



The meganucleus is undoubtedly somatic in function. The 

 experiments mentioned on p. 392 prove that it is essential for the 

 process of the repair of injuries and for the restoration of parts 

 that have been lost; the changes in the structure of its granules 

 observed during assimilation and starvation point to its important 

 relations with the processes of digestion, whilst the changes in 

 its shape and position, during the somatic life of the individual, 

 indicate its continued functional activity during this period. 



Speaking generally of the meganucleus of the Heterokaryotes, 

 it may be remarked that, as compared with other nuclei, it exhibits 

 an extraordinary variety of form. It may be spherical, oval, band- 

 like, moniliform, dumb-bell shaped, double, or scattered in numerous 

 small fragments. 



The exact meaning of this may be obscure, but it is quite 

 consistent with the facts to believe that its peculiar shapes are 

 associated with the important somatic functions, over which it 

 exercises some essential control. 



Whilst it is thus clear that the meganucleus is somatic in 

 function, it is none the less evident that the micronucleus is not. 



