GENERAL SKETCH 



57 



Simple division frequently leads to colony-formation through incom- 

 plete separation of the daughter-individuals. Four general types of 

 these colonies are met with among the Protozoa. Adopting Haeckel's 

 terms, they may be designated according to their general structure as 

 (l) gregaloid, (2) spheroid, (3) arboroid, and (4) catenoid. 



A gregaloid colony is an aggregate of Protozoa having a round, 

 ellipsoidal, or indefinite shape, and usually with a gelatinous basis in 

 which the single individuals are variously distributed. The colonies 

 may be formed by incomplete division of the individuals or by partial 

 union of two or more adults (Fig. 24). A spheroid colony is a globu- 



Fig. 26. — Codosiga cymosa Sav. K., an arboroid colony of Choanoflagellida. [Kent.] 



lar, ellipsoidal, or cylindrical aggregate in which the individual cells 

 form a superficial layer in a common gelatinous matrix. When these 

 superficial cells are closely packed together into an almost continuous 

 layer as in Volvox, Magosphcera, or Uroglena, they are extremely sug- 

 gestive of certain stages in developing Metazoa (Fig. 25). An arbo- 

 roid colony is a tree- or bush-like aggregate arising by the dendritic 

 or dichotomous branching of a primary stalk or a gelatinous matrix. 

 Such colonies are usually attached by the base to some foreign object 

 and often resemble hydroids or Bryozoa (Fig. 26). They may, how- 

 ever, as in Dinobryon, be free-swimming. A catenoid colony is fili- 

 form or chain-shaped, arising from the union of cells end to end, or 



