132 



GENERAL BIOLOGY 



attached to one another in chains or masses. Such 

 a mass might justly be called a tissue, except that it 

 is convenient to restrict the use of that term to a 

 cell-mass which, in turn, is a part of a still more 

 highly organized complex. In certain Algae this 

 connection of cells with one another is transitory 

 and indefinite. In some forms, however, the con- 

 nection is permanent, 

 and the mass con- 

 sists of a definite 

 number of cells. In 

 such a case we speak 

 of the cell group as 

 a colony. The com- 

 bination of individ- 

 uals in a colony is 

 not only found in the 

 Protista, but in many 

 of the higher groups 

 as well, particularly 

 in such forms as are 

 fixed to one spot (sea squirts, coelenterates, sponges, 

 and most plants). 



Fission in Metazoa. Not only in the Protista, 

 but in metazoa also, are found examples of repro- 

 duction by fission. In Ctenodrilus, one of the lower 

 Annelids, the worm cuts in two by transverse fission 

 much as an elongated protozoan. The separate por- 

 tions of the original body then become transformed 

 into complete individuals by a shifting and read- 



FIG. 47. Budding in an animal 

 (Clavelina). The individual organisms 

 develop from an outgrowth of the body- 

 wall analogous to a plant rootstalk. 

 Natural size. (Herdman.) 



