General Morphology of the Protozoa 7 



Eudorina, Gonium, and Pandorina may undergo fission and produce 

 daughter colonies (11). The component flagellates of the Volvox colony 

 are differentiated into somatic and reproductive individuals and the 

 former are believed to lose their reproductive ability when the colony 

 reaches maturity. 



Protozoan colonies are usually classified on the basis of their organiza- 

 tion. Spheroid and discoid colonies, containing a matrix secreted by the 

 associated organisms during development of the colony, are represented 

 by such ciliates as Ophrydium and various flagellates — Syncrypta, Go- 

 nium, Pandorina, Volvox, and others. In Gonium sociale, for example, the 

 matrix shows two components (Fig. 1. 2, C), a "cell wall" enclosing each 

 flagellate and a continuous outer gelatinous layer. In some specimens (Fig. 

 1. 2, A, B) the outer layer is lacking. Each flagellate in the Volvox colony 

 is enclosed in a thin cell wall and a thick outer sheath. Except in V. 

 aureus, the boundaries of the individual sheaths are readily distinguished. 

 The flagellates appear to be joined by protoplasmic strands in certain 

 species of Volvox (Fig. 1. 2, G) and apparently also in Eudorina, Gonium, 

 and Pandorina (11). Dried colonies of Gonium (Fig. 1. 2, D, E), after 

 silver impregnation, show "silver-line" connections between adjacent 

 flagellates (131). 



In arboroid colonies (Fig. 1. 3), the individual organisms are arranged 

 in a branching pattern. Stalks are characteristic of many arboroid colonies. 

 In different species, each organism may have its own stem which is at- 

 tached to a common stalk, or each stalk of the framework may bear more 

 than one organism. Such stalks may be gelatinous or sometimes solid and 

 relatively firm, and in certain cases they are elastic tubes containing 

 contractile fibrils. In other arboroid types, colonial organization is main- 

 tained by attachment of one lorica to another (Fig. 1. 3, C, D), or by a 

 continuous tubular "lorica" in which the organisms are located at the 

 tips of the branches (Fig. 1. 3, E). 



NON-COLONIAL GROUPINGS 



Certain other aggregates are not colonies in the strict sense. So- 

 called catenoid colonies have been described in dinoflagellates (Fig. 1. 

 4, D) and certain astomatous ciliates (Fig. 1. 4, C). These chains arise in 

 repeated fission without prompt separation of daughter organisms and 

 are temporary groupings rather than true colonies. Palmella stages (Fig. 1. 

 4, A) of certain flagellates develop in much the same manner as spheroid 

 and discoid colonies. However, the palmella does not show a well defined 

 range in size, the number of organisms varies with size of the mass, and 

 the flagellates lack flagella. The term, gleocystis stage, is sometimes applied 

 to similar aggregates in which an individual gelatinous layer surrounds 

 each organism (Fig. 1. 4, B). 



